Brewster angle microscopy study of poly(epsilon-caprolactone) crystal growth in Langmuir films at the air/water interface

Surface pressure-induced crystallization of poly(epsilon-caprolactone) (PCL) from a metastable region of the surface pressure-area per monomer (Pi-A) isotherm in Langmuir monolayers at the air/water (A/W) interface has been captured in real time by Brewster angle microscopy (BAM). Morphological features of PCL crystals grown in Langmuir films during the compression process exhibit four fully developed faces and two distorted faces. During expansion of the crystallized film, polymer chains slowly detach from the crystalline domains and diffuse back into the monolayer as the crystals "melt". Typical diffusion-controlled morphologies are revealed by BAM during the melting process as the secondary dendrites melt away faster, that is, at a higher surface pressure than the principal axes. Electron diffraction on Langmuir-Schaefer films suggests that the lamellar crystals are oriented with the polymer chain axes perpendicular to the substrate surface, while atomic force microscopy reveals a crystal thickness of approximately 7.6 nm.     

Blends of amphiphilic poly(dimethylsiloxane) and nonamphiphilic octaisobutyl-POSS at the air/water interface

Brewster angle microscopy (BAM) shows that a nonamphiphilic polyhedral oligomeric silsesquioxane (POSS) nanofiller, octaisobutyl-POSS, forms aggregates at all surface concentrations at the air/water interface. When amphiphilic poly(dimethylsiloxane) (PDMS) is blended with the octaisobutyl-POSS (>10 wt % PDMS), the degree of POSS aggregation dramatically decreases. Thermodynamic analyses and morphology studies through surface pressure-area per monomer isotherm data and BAM, respectively, exhibit three distinct composition regimes: (1) Blends with >70 wt % POSS have unstable isotherms whose shapes deviate from those of PDMS and form large rigid domains comparable to but smaller than pure, octaisobutyl-POSS films. (2) At compositions between approximately 40 and 70 wt % POSS, the isotherms' features are qualitatively similar to those of pure PDMS, and extensive nanofiller "networks" are observed by BAM. (3) For compositions < or = approximately 30 wt % POSS, the isotherms are essentially those of pure PDMS with small POSS domains dispersed in the PDMS matrix. These results provide further insight into nanofiller aggregation mechanisms and dispersion that may be present in thicker films and bulk systems.     

Vertical phase separation and liquid-liquid dewetting of thin PS/PCL blend films during spin coating

Thin films of an amorphous polymer, polystyrene (PS), and a crystalline polymer, poly(ε-caprolactone) (PCL), blend were prepared by spin coating a toluene solution. Surface chemical compositions of the blend films were measured by X-ray photoelectron spectroscopy (XPS), and the surface and interface topographical changes were followed by atomic force microscopy (AFM). By changing the PS concentration and keeping the PCL concentration of the solution at 1 wt %, a great variety of morphologies were constructed. The results show that the morphology of the blend films can be divided into three regions with increasing PS concentration. In region I, PS island domains are embedded in PCL crystals when the PS concentration is lower than 0.3 wt % and the size of the PS island increases with increasing PS concentration. In region II, holes with different sizes surrounded by a low rim are obtained when the concentration of PS is between 0.35 and 0.5 wt %. After selectively washing the PS domains, we studied the interface morphology of PS/PCL and found that the upper PS-rich layer extended into the bottom PCL layer, forming a trench surrounding the holes. In region III, an enriched two-layer structure with the PS-rich layer on top of the blend films and the PCL-rich crystal layer underneath is obtained when the concentration of PS is higher than 0.5 wt %. Last, the formation mechanism of the different surface and interface morphologies is further discussed in terms of the vertical phase separation to a layered structure, followed by liquid-liquid dewetting and crystallization processes during spin coating.     

Blends of amphiphilic trisilanolisobutyl-POSS and phosphine oxide substituted poly(dimethylsiloxane) at the air/water interface

Mixtures of a polyhedral oligomeric silsesquioxane, trisilanolisobutyl-POSS, and a polar silicone, poly(dimethyl-co-methylvinyl-co-methyl, 2-diphenyl phosphine oxide ethyl) siloxane (PDMS-PO), spread as Langmuir monolayers at the air/water interface are used to examine the surface phase behavior and aggregation of trisilanolisobutyl-POSS as a function of silicone composition. Analyses of the surface pressure-area per monomer (Pi-A) isotherms in terms of the collapse pressures and excess Gibbs free energies of mixing indicate the monolayers form slightly negative deviation mixtures. Direct observations of surface morphology with Brewster angle microscopy in the collapsed regime reveal that the governing factor for aggregation is the collapse Pi of the component with a stronger affinity for water. In trisilanolisobutyl-POSS/PDMS-PO blends, POSS aggregates as discrete domains and does not coalesce into larger aggregates or networklike structures for <80 wt % POSS, a feature that is vastly different from a previous study of POSS blended with regular poly(dimethylsiloxane).     

Two-dimensional self-assembly of linear poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers at the air-water interface

The interfacial properties of amphiphilic linear diblock copolymers based on poly(ethylene oxide) and poly(epsilon-caprolactone) (PEO-b-PCL) were studied at the air-water (A/W) interface by surface pressure measurements (isotherms and hysteresis experiments). The resulting Langmuir monolayers were transferred onto mica substrates and the Langmuir-Blodgett (LB) film morphologies were investigated by atomic force microscopy (AFM). All block copolymers had the same PEO segment (Mn = 2670 g/mol) and different PCL chain lengths (Mn = 1270; 2110; 3110 and 4010 g/mol). Isothermal characterization of the block copolymer samples indicated the presence of three distinct phase transitions around 6.5, 10.5, and 13.5 mN/m. The phase transitions at 6.5 and 13.5 mN/m correspond to the dissolution of the PEO segments in the water subphase and crystallization of the PCL blocks above the interface similarly as for the corresponding homopolymers, respectively. The phase transition at 10.5 mN/m was not observed for the homopolymers alone or for their blends and arises from a brush formation of the PEO segments anchored underneath the adsorbed hydrophobic PCL segments. AFM analysis confirmed the presence of PCL crystals in the LB films with unusual hairlike/needlelike architectures significantly different from those obtained for PCL homopolymers.     

Phase behavior and viscoelastic properties of trisilanolcyclohexyl-POSS at the air/water interface

A trisilanol polyhedral oligomeric silsesquioxane (POSS), trisilanolcyclohexyl-POSS (TCyP), has recently been reported to undergo a series of phase transitions from traditional Langmuir monolayers to unique rodlike hydrophobic aggregates in multilayer films that are different from "collapsed" morphologies seen in other systems at the air/water interface. This paper focuses on the phase transitions and morphology of films varying in average thickness from monolayers to trilayers and the corresponding viscoelastic properties of trisilanolcyclohexyl-POSS molecules at the air/water interface by means of surface pressure-area per molecule (Pi-A) isotherms, Brewster angle microscopy (BAM), and interfacial stress rheometry (ISR) measurements. The morphology studies by BAM reveal that the TCyP monolayer can collapse into different 3D structures by homogeneous or heterogeneous nucleation mechanisms. For homogeneous nucleation, analysis by Vollhardt et al.'s nucleation and growth model reveals that TCyP collapse is consistent with instantaneous nucleation with hemispherical edge growth at Pi = 3.7 mN.m(-1). Both surface storage (Gs') and loss (Gs") moduli obtained by ISR reveal three different non-Newtonian flow regimes that correlate with phase transitions in the Pi-A isotherms: (A) A viscous liquidlike "monolayer"; (B) a "biphasic regime"between a liquidlike viscous monolayer and a more rigid trilayer; and (C) an elastic solidlike "trilayer". These observations provide interesting insights into collapse mechanisms and structures in Langmuir films.     

Dendritic growth of poly(ε-caprolactone) crystals from compatible blends with poly(t-butyl acrylate) at the air/water interface

Thermodynamic analyses of surface pressure-area (Π-A) isotherms and Brewster angle microscopy (BAM) reveal that poly(ε-caprolactone) (PCL) with a weight average molar mass of M_w = 10 kg mol⁻¹ and polydispersity index of M_w/M_n = 1.25 and poly(t-butyl acrylate) (PtBA, M_w = 25.7 kg mol⁻¹; M_w/M_n = 1.07) form compatible blends as Langmuir films below the dynamic collapse transition for PCL at Π = 11 mN m⁻¹. For PCL-rich blends, in situ BAM studies reveal growth of PCL crystals for compression past the PCL collapse transition. PCL crystals grown in the plateau regime of the Π-A isotherm exhibit a dendritic morphology presumably resulting from the rejection of PtBA from the growing PCL crystals and hindered diffusion of PCL from the surrounding monolayer to the crystal growth fronts. The ability to transfer the PCL dendrites as Langmuir–Schaefer films onto silicon substrates spincoated with a polystyrene layer facilitates detailed morphological characterization by optical and atomic force microscopy (AFM). AFM reveals that the dendritic branching occurs along the {100} and {110} sector boundaries and is essentially independent of composition. AFM also reveals that the average thickness of PCL dendrites formed at room temperature (22.5 °C), ∼7–8 nm, is comparable with that of PCL crystals grown from single-component PCL Langmuir films and spincoated thin films. In contrast, for PtBA-rich blend films PCL crystallization is suppressed. These findings establish PCL blends as an ideal system for exploring the interplay between chain diffusion and crystal growth in a two-dimensional confined geometry. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3300–3318, 2007     

Polyhedral oligomeric silsesquioxanes: a new class of amphiphiles at the air/water interface

Insoluble films of trisilanolisobutyl-POSS and octaisobutyl-POSS at the air/water interface are investigated by means of surface pressure - area per molecule isotherm (Pi - A) and Brewster angle microscopy (BAM). Analysis of the experimental results shows the partial cage molecule, trisilanolisobutyl-POSS, is a surface-active molecule that self-assembles into uniform monolayer upon compression; but the fully condensed cage molecule, octaisobutyl-POSS, is nonamphiphilic.     

Langmuir and Langmuir-Blodgett films of poly(ethylene oxide)-b-poly(epsilon-caprolactone) star-shaped block copolymers

Self-assembly of poly(ethylene oxide)-block-poly(epsilon-caprolactone) five-arm stars (PEO-b-PCL) was studied at the air/water (A/W) interface. The block copolymers consist of a hydrophilic PEO core with hydrophobic PCL chains at the star periphery. All the polymers have the same number of ethylene oxide repeat units (9 per arm), and the number of epsilon-caprolactone repeat units ranges from 0 to 18 per arm. The Langmuir monolayers were analyzed by surface pressure/mean molecular area isotherms, compression-expansion hysteresis experiments, and isobaric relaxation measurements, and the Langmuir-Blodgett (LB) films' morphologies were investigated by atomic force microscopy (AFM). PCL homopolymers crystallize directly at the A/W interface in a narrow surface pressure range (11-15 mN/m). In the same pressure region, the star-shaped block copolymers undergo a phase transition corresponding to the collapse and the crystallization of the PCL chains as shown by the presence of a pseudoplateau in the isotherms. The LB films were prepared by transferring the Langmuir monolayers onto mica substrates at various surface pressures. AFM imaging confirmed the formation of PCL crystals in the LB monolayers of the PCL homopolymers and of the copolymers, but also showed that the PCL segments can undergo additional crystallization after monolayer transfer during water evaporation. The PCL crystal morphologies were also strongly influenced by the surface pressure and by the PEO segments.     

Surface segregation of polypeptide-based block copolymer micelles: An approach to engineer nanostructured and stimuli responsive surfaces

We describe the surface segregation of polypeptide-based block copolymer micelles to produce stimuli-responsive nanostructures at the polymer blend/air interface. Such structures were obtained by simultaneous surface migration and self assembly at the surface of diblock copolymer/homopolymer blends. We employed blends composed of homopolymer (PS) and an amphiphilic block copolymer polystyrene-b-poly(l-glutamic acid) (PS-b-PGA). The surface was functionalized based on the preferential segregation to the polymer blend/air interface of the hydrophilic PGA block of the diblock copolymer upon annealing to water vapor. The surface migration of the diblock copolymer to the interface was demonstrated both by XPS and contact angle measurements. As a consequence, the PGA interfacial attraction leads to a large surface excess on diblock copolymer which in turn, through macrophase and microphase separation, produced separated domains at the surface with regions composed either of homo or block copolymer. Herein we demonstrate that the use of asymmetric diblock copolymers with a higher content in PS lead to spherical micellar assemblies randomly distributed at the surface. As observed by AFM imaging the blend composition, i.e. the amount of block copolymer within the blend influences the density of micelles at the surface. Finally, when exposed to water, the pH affects the surface morphology. The PGA segments are collapsed at low pH values and extended at pH values above 4.8, thus inducing variations on the topography of the films at the nanometer scale.     

Irreversible Collapse of Poly(vinyl stearate) Monolayers at the Air-Water Interface

The collapse of Langmuir monolayers of poly(vinyl stearate) (PVS) at the air-water interface has been investigated by combined measurements of the surface pressure-area isotherms and Brewster angle microscopy (BAM). Atomic force microscopy (AFM) has been used to gain out-of-plane structural information on collapsed films transferred onto a solid substrate by a modified version of the inverse Langmuir-Schaefer deposition method. At high areas per monomer repeat unit, BAM imaging revealed that the films are heterogeneous, with large solidlike domains (25-200 mum in diameter) coexisting with liquidlike domains. Upon film compression, the domains coalesced to form a homogeneous monolayer before the film collapsed at constant pressure, forming irreversible three-dimensional (3D) structures. BAM images showed that two 3D structures coexisted: buckles of varying width extending across the surface and perpendicular to the direction of the compression and dotted islandlike structures. Upon expansion, the film fractured and both 3D protrusions persisted, explaining the marked hysteresis recorded in the Langmuir isotherms. Experiments with AFM confirmed the 3D nature of both protrusions and revealed that many buckles contain substructures corresponding to narrow buckles whose heights are a multiple of a single bilayer. Additionally, many multilayer islands with diameters spanning from 0.2 mum to over 3.5 mum were characterized by varying heights between 2 nm and up to over 50 nm. The key to the formation of the irreversible 3D structures is the presence of large inhomogeneities in the PVS monolayer, and a generalized phenomenological model is proposed to explain the collapse observed.     

Pure and mixed films of a nitrostilbene derivative at the air-water interface, Langmuir-Blodgett multilayer fabrication, and optical characterization

This paper reports the preparation and characterization of pure Langmuir and Langmuir-Blodgett (LB) films of a stilbene derivative containing two alkyl chains, namely 4-dioctadecylamino-4'-nitrostilbene. Mixed films incorporating docosanoic acid and the stilbene derivative are also studied. Brewster angle microscopy (BAM) analysis has revealed the existence of randomly oriented three-dimensional (3D) aggregates, spontaneously formed immediately after the spreading process of the stilbene derivative onto the water surface. These 3D aggregates coexist with a Langmuir film that shows the typical gas, liquid, and solid-like phases in the surface pressure and surface potential vs area per molecule isotherms, indicative of an average preferential orientation of the stilbene compound at the air-water interface, and a gradual molecular arrangement into a defined structure upon compression. A blue shift of 55 nm of the reflection spectrum of the Langmuir film with respect to the spectrum of a chloroform solution of the nitrostilbene indicates that two-dimensional (2D) H-aggregates are formed at the air-water interface. The monolayers are transferred undisturbed onto solid substrates with atomic force microscopy (AFM) revealing that the one layer LB films are constituted by a monolayer of the stilbene derivative together with some 3D aggregates. When the nitrostilbene compound is blended with docosanoic acid, the 3D aggregation is avoided in the Langmuir and Langmuir-Blodgett films, but does not limit the formation of 2D H-aggregates, desirable for second-order nonlinear optical response in the blue domain. The AFM images of the mixed LB films show that they are formed by a docosanoic acid monolayer and, on the top of it, a bilayer of the stilbene derivative.     

Brewster angle microscopic observations of the Langmuir films of amphiphilic spiropyran during compression and under UV illumination

The structure of the Langmuir film of an amphiphilic spiropyran, 1',3'-dihydro-3',3'-dimethyl-6-nitro-l'-octadecyl-8-(docosanoyloxyme thyl)spiro[2H-1-benzopyran-2,2'-(2H)-indole] (SP), is investigated using Brewster angle microscopy (BAM). The BAM observations show that the Langmuir film of SP can be roughly categorized into three regimes: a low-temperature regime at 7-13 degrees C; a medium-temperature regime at 23-30 degrees C; a high-temperature regime at 40 degrees C. The low-temperature regime is characterized both by the domains that are formed just after the spreading and by the onset of the surface pressure when the domains are merged together to form continuous trilayers. In the medium-temperature regime, a continuous monolayer film is formed after the solvent evaporation, followed by the growth of "embryos" with compression. Around the phase transition point, the "embryos" serve as the "nucleation sites" of the circular trilayer domains. The characteristic features of the high-temperature regime are similar to the ones of the medium-temperature regime except for the absence of a steep rise in surface pressure after the plateau region and the absence of the circular trilayer domains. UV illumination of the Langmuir films leads to the isomerization of SP into merocyanine (MC). However, J-aggregates of MC are formed only when the circular trilayer domains are present. On the basis of the above results, we present a phase diagram of the Langmuir film of SP. The structure and photoreaction depend strongly on the phase of the Langmuir film, indicating that the area/molecule is not the only decisive parameter.     

Surface phase separation, dewetting feature size, and crystal morphology in thin films of polystyrene/poly(ε-caprolactone) blend

Thin films of polystyrene (PS)/poly(ε-caprolactone) (PCL) blends were prepared by spin-coating and characterized by tapping mode force microscopy (AFM). Effects of the relative concentration of PS in polymer solution on the surface phase separation and dewetting feature size of the blend films were systematically studied. Due to the coupling of phase separation, dewetting, and crystallization of the blend films with the evaporation of solvent during spin-coating, different size of PS islands decorated with various PCL crystal structures including spherulite-like, flat-on individual lamellae, and flat-on dendritic crystal were obtained in the blend films by changing the film composition. The average distance of PS islands was shown to increase with the relative concentration of PS in casting solution. For a given ratio of PS/PCL, the feature size of PS appeared to increase linearly with the square of PS concentration while the PCL concentration only determined the crystal morphology of the blend films with no influence on the upper PS domain features. This is explained in terms of vertical phase separation and spinodal dewetting of the PS rich layer from the underlying PCL rich layer, leading to the upper PS dewetting process and the underlying PCL crystalline process to be mutually independent.     

玻璃基板作用下高分子共混物薄膜相形态发展过程

研究了玻璃基板作用下极性高聚物为低组分的共混物薄膜在退火条件下相形态的发展过程 .选用聚苯乙烯 (PS) 聚甲基丙烯酸甲酯 (PMMA)与聚苯乙烯 (PS) 聚ε 己内酯 (PCL)两个体系 ,在玻璃基板上Spin Coating成膜后退火 .由于共混物薄膜中极性相对较大的高聚物组分 (PMMA和PCL)相对于极性较小的PS组分对玻璃基板具有更好的润湿性 ,所以在上述的两个共混薄膜体系中其相形态分别显示PMMA和PCL在低组分比例下最终发展成为连续相 .利用扫描电镜以及元素分析很好地验证了以上的结论 ,并且对其机理进行了解释 .此外 ,改变PS的分子量与PCL共混 ,研究了组分粘度对薄膜相形态发展的影响 .结果表明 ,PS组分粘度越大 ,共混物薄膜相结构发展速度越慢     

Langmuir monolayers of bent-core molecules

A systematic study of five different, symmetric bent-core liquid crystals in Langmuir thin films at the air/water interface is presented. Both the end chains (siloxane vs hydrocarbon) and the core (more or less amphiphilic) are varied, to allow an exploration of different possible layer structures at the interface. The characterization includes systematic surface pressure isotherms, Brewster angle microscopy, and surface potential measurements. The properties of these layers are strongly dependent on the individual type of molecule: the molecules with amphiphilic end chains lie quite flat on the surface, while the molecules with hydrophobic end chains construct multilayer structures. In both cases, the three-dimensional collapse structure is reversible.     

Self-assembly of polystyrene-block-poly(ethylene oxide) copolymers at the air-water interface: is dewetting the genesis of surface aggregate formation?

Block copolymer self-assembly at the air-water interface is commonly regarded as a two-dimensional counterpart of equilibrium block copolymer self-assembly in solution and in the bulk; however, the present analysis of atomic force microscopy (AFM) and isotherm data at different spreading concentrations suggests a nonequilibrium mechanism for the formation of various polystyrene-b-poly(ethylene oxide) (PS-b-PEO) aggregates (spaghetti, dots, rings, and chainlike aggregates) at the air-water interface starting with an initial dewetting of the copolymer spreading solution from the water surface. We show that different spreading concentrations provide kinetic snapshots of various stages of self-assembly at the air-water interface as a result of different degrees of PS chain entanglements in the spreading solution. Two block copolymers are investigated: MW = 141k (11.4 wt % PEO) and MW = 185k (18.9 wt % PEO). Langmuir compression isotherms for the 185k sample deposited from a range of spreading concentrations (0.1-2.0 mg/mL) indicate less dense packing of copolymer chains within aggregate cores formed at lower spreading concentrations due to a competition between the interfacial adsorption of PEO blocks and the kinetic restrictions of PS chain entanglements. From AFM analysis of the transferred Langmuir-Blodgett films, it is clear that PS chain entanglements in the spreading solution also affect the morphological evolution of surface aggregates for both samples, with earlier structures being trapped at higher concentrations. At the highest spreading concentration for the 141k copolymer, the coexistence of long spaghetti aggregates with cellular arrays of holes, along with various transition structures, indicates that various surface aggregates evolve from networks of rims formed as a result of dewetting of the evaporating spreading solution from the water surface.     

The behavior of poly(ε -caprolactone) and poly(ethylene oxide)-b-poly(ε -caprolactone) grafted to a poly(glycerol adipate) backbone at the air/water interface

The behavior of crystallizable poly(ε-caprolactone) (PCL) and poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) is studied at the air/water interface prior and after grafting to an amorphous poly(glycerol adipate) (PGA) backbone (PGA-g-PCL, PGA-g-(PCL-b-PEO)). Langmuir isotherms are measured and the structure formation in the monolayers on the water surface is followed by Brewster angle microscopy (BAM) and in Langmuir–Blodgett films after a transfer to silicon substrates by atomic force microscopy (AFM). It is observed that PGA-g-PCL forms significantly smaller crystals on the water surface and has smaller crystallization rate compared to PCL homopolymers of identical molar masses as the grafted chains. In contrast to crystals formed by linear PCL, the crystals formed by grafted PCL in PGA-g-PCL do not melt (readsorb at the water surface) in an expansion cycle on the Langmuir trough. Additionally, increasing the subphase temperature at constant surface area significantly above the melting point of linear PCL in bulk results in the formation of a mesophase, and it does lead to the disappearance of crystals. The isotherms of PGA-g-(PCL-b-PEO) show a transition at the surface pressure of ～10 mN/m. This is related to the fact that PEO chains leave the water surface and submerge into the subphase and/or the crystallization of PCL chains. The monolayer collapse appears in an extended plateau region starting at π values of ～30 mN/m. AFM images of Langmuir–Blodgett films reveal that PCL chains in PGA-g-PCL and PGA-g-(PCL-b-PEO) form lamellar crystals with a disk-shape and interconnected platelets, respectively.     

Surface morphologies of Langmuir-Blodgett monolayers of PEOnPSn multiarm star copolymers

Star polymers composed of equal numbers of poly(ethylene oxide) (PEO) and polystyrene (PS) arms with variable lengths and a large (up to 38 total) number of arms, PEO(n)PS(n), have been examined for their ability to form domain nanostructures at the air-water and air-solid interfaces. All PEO(n)PS(n) star polymers formed stable Langmuir-Blodgett (LB) monolayers transferable to a solid substrate. A range of nanoscale surface morphologies have been observed, ranging from cylindrical to circular domains to bicontinuous structures as the weight fraction of the PEO block varied from 19% to 88% and n from 8 to 19. For the PS-rich stars and at elevated surface pressure, a two-dimensional supramolecular netlike nanostructure was formed. In contrast, in the PEO-rich star polymer with the highest PEO content, we observed peculiar dendritic superstructures caused by intramolecular segregation of nonspherical core-shell micellar structures. On the basis of Langmuir isotherms and observed monolayer morphologies, three different models of possible surface behavior of the star polymers at the interfaces were proposed.     

Brewster angle microscopy: A preferential method for mesoscopic characterization of monolayers at the air/water interface

Knowledge of the mesoscopic morphology of condensed phase domains formed after the main phase transition in the two-phase coexistence region of Langmuir monolayers progressed rapidly with the development of the highly-sensitive imaging techniques, particularly by Brewster angle microscopy (BAM). Latest developments of commercial BAM instruments have been developed to a high technical level and allow upgrading to imaging ellipsometers which combine optical microscopy and ellipsometry and make the assessment of small layered structures or patterned thin films possible. A large variety of condensed phase domains different in mesoscopic sizes and shapes as well as their textural features has been observed which depend sensitively on the chemical structure of the amphiphilic monolayer and the system conditions, such as surface pressure and temperature. This unsuspected morphological variety of condensed phase domains has been proven not only in Langmuir monolayers but also in adsorbed monolayers (Gibbs monolayers), in Langmuir monolayers penetrated by dissolved surfactants or in adequate molecular recognition systems. The inner textures of domains can be explained on the basis of their geometry and the two-dimensional lattice in dependence of the tilt angle of the alkyl chains and gave rise to the development of a geometric concept on the basis of the molecular packing. New knowledge has been gained about non-equilibrium structures and their transition kinetics into the equilibrium state. Combined results obtained recently by BAM have enhanced the understanding of molecular organization in phase diagrams and binary mixtures. Recent advances in model studies about chiral discrimination effects and of the highly specific structural changes of host-monolayers by recognition of non-surface active guest-components have made progress. Semi-empirical quantum chemical methods have been used to gain insight into the role of different types of interactions involved in the main characteristics of mesoscopic length scale aggregates of mimetic systems.