Insight into diacetylene photopolymerization in Langmuir‐Blodgett films using simultaneous AFM and fluorescence microscopy imaging

A phase‐separated monolayer film comprised of a mixture of 10, 12‐pentacosadiynoic acid (PCDA) with perfluorotetradecanoic acid (PF; CF₃(CF₂)₁₂COOH) has been characterized using a microscope that is capable of simultaneous atomic force microscope (AFM) imaging and fluorescence imaging. Design criteria for this instrument are described, as well as its application to investigating the mixed film systems. The product of PCDA photopolymerization has two phases, a red phase with strong fluorescence and a blue phase with no fluorescence. With the help of the dual AFM‐fluorescence microscope, it was found that both the red and the blue phase polymers were produced in the same sample from photoillumination, and the relative quantities of the different phases were quantified. Further, the importance of intrinsic mechanical stress in the films is discussed in terms of its influence on selectivity towards the red polymer phase.     

Langmuir monolayers and Langmuir–Blodgett films of 1-acyl-1,2,4-triazoles

New 1-acyl-1,2,4-triazoles (ATs) with different n-alkyl chain lengths from C2 to C18 were synthesized. ATs with long n-alkyl chains (C12 and larger) are non-charged amphiphilic molecules with a polar triazole head group. The Langmuir isotherms of ATs at the air–water interface with 12 (DoT-C12), 14 (MyT-C14), 16 (PaT-C16) and 18 (StT-C18) carbon atoms in their n-alkyl chains were studied using surface pressure-mean molecular area (π-mmA) measurements. Characteristic for the Langmuir isotherms of PaT-C16 and StT-C-18 was the first sharp increase of the surface pressure at a mmA value of 20 Å² marking a transition of the ATs from the gaseous state with n-alkyl chains already oriented perpendicular to the water surface to a condensed state. The collapse of the monolayers occurred between 20 and 36 mN m⁻¹ with a typical ‘spike’ in the isotherms of MyT-C14, PaT-C16 and StT-C18 which can be assigned to the buckling and subsequent folding of the monolayer. After the collapse point a pseudo-plateau region of slightly increasing surface pressure appeared for all ATs from C12 to C18 indicating a trilayer formation by the roll-over mechanism for MyT-C14, PaT-C16 and StT-C18. Upon further compression the final collapse occurred at π values between 59 and 67 mN m⁻¹. From reversibility studies it was found that the Langmuir isotherms of the ATs were irreversible. The morphology of Langmuir–Blodgett films of ATs transferred onto silicon wafers was studied by atomic force microscopy.     

Phosphorus‐nitrogen compounds. Part 39. Syntheses and Langmuir‐Blodgett thin films and antimicrobial activities of N/N and N/O spirocyclotriphosphazenes with monoferrocenyl pendant arm

The Cl substitution reactions of the N/N ( 1 ‐ 3 ) and N/O ( 4 and 5 ) spirocyclic monoferrocenylphosphazenes with 1,4‐dioxa‐8‐azaspiro[4,5]decane (DASD) produce the mono‐ ( 1a ‐ 5a ), geminal‐ ( 1b ‐ 5b ) and tetrakis‐DASD‐substituted ferrocenylspirocyclotriphosphazenes ( 1c ‐ 5c ). The mono‐ and geminal‐DASD‐substituted phosphazenes have two and one stereogenic P‐centers, respectively. The structures of the compounds were established by spectroscopic techniques. The molecular structures of 3a and 2b were evaluated using X‐ray crystallography. Additionally, the ultrathin and highly ordered Langmuir‐Blodgett (LB) films of 3a and 2b were also prepared. The characterizations of the LB films were done using p‐polarized grazing angle (GAIR) and horizontal attenuated total reflectance (HATR) techniques. On the other hand, the antimicrobial activities of the eight phosphazene derivatives against G(+) and G(‐) bacteria and fungi were investigated. Furthermore, the interactions between the compounds and plasmid DNA were studied by agarose gel electrophoresis.     

Langmuir‐Blodgett Films of Alkanethiolate Gold Nanorods

Colloidal multilayers of octadecanethiol‐capped Au nanorods were prepared using the Langmuir‐Blodgett technique. Uniform growth of the films with increasing number of deposition has been observed. Vertical transfer efficiency indicates efficient transfer for immersion of hydrophobic substrates and poor transfer for emersion of such substrates. The vertically transferred film has an order parameter S = 0.027, which suggests that the orientation of the nanorods in the film is somewhat isotropic about the dipping direction. Horizontal transfer of the Langmuir monolayer on Formvar/carbon‐coated Cu grids, however, gave scattered domains of Au nanorods aligned in parallel stacks. Such behavior is probably related to the rigidity of the Langmuir monolayer.     

Functionalized Gold Nanoparticles – Octadecylamine Hybrid Langmuir‐Blodgett Film for Enzyme Sensor

Mediator free enzyme sensor has been fabricated by covalently immobilizing cholesterol oxidase (ChOx) onto 11‐mercaptoundecanoic acid functionalized gold nanoparticles (MUDA‐AuNPs) – octadecylamine (ODA) hybrid Langmuir–Blodgett film. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) studies reveal that MUDA‐AuNP/ODA LB film has good affinity for ChOx and provides favorable microenvironment for direct electron transfer between enzyme and electrode. Interference free estimation of cholesterol has been realized at 0.3 V with linear range from 25 to 500 mg/dL, detection limit of 23.38 mg/dL, sensitivity of 1.085 μA mM^?1 and response time of 20 s at pH 7.0.     

Induction of Ring‐Shaped Calcium Oxalate Patterns by Boundaries between Liquid Expanded Phase and Liquid Condensed Phase in Langmuir‐Blodgett Film

The formation of calcium oxalate kidney stones was related to injuries of renal epithelial membranes. The liquid condensed (LC) domains in Langmuir‐Blodgett (LB) film of dipalmitoylphosphatidylcholine (DPPC) were used as a model system to induce crystal growth of urinary mineral calcium oxalate monohydrate (COM). The circular defective boundaries between the LC and liquid expanded (LE) phases of the DPPC monolayer could provide much more nucleating sites for crystallization of COM crystals. It induced ring‐shaped or solid circular patterns of COM crystals on hydrophobic quartz substrates depending on the crystallization time.     

Removal of poly(methyl methacrylate) in diblock copolymers films studied by grazing incidence small‐angle X‐ray scattering

Self‐assembly of diblock copolymers (BCP) into periodic arrays is a promising route to generate templates for the fabrication of nanoscopic elements, when one block is selectively removed. In cylindrical morphology polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) copolymer (BCP) films, the efficiency of different processes for removing the PMMA from cylinders is studied using grazing incidence small angle X‐ray scattering (GISAXS), x‐ray reflectivity and critical dimension scanning electron microscopy. The detailed analysis of the GISAXS patterns leads to the determination of the depth of cylindrical holes left by removal of the PMMA. It is found that the combination of a preliminary UV exposure followed by a wet treatment allows to remove totally the PMMA blocks. Furthermore, the optimization of both UV exposition time and solvent allows to preserve the PS matrix and interestingly for nanolithographic applications to decrease the process costs. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1137–1144     

Luminescent Amphiphilic 2,6‐Bis(1‐alkylpyrazol‐3‐yl)pyridyl Platinum(II) Complexes: Synthesis,Characterization, Electrochemical,Photophysical, and Langmuir–Blodgett Film Formation Studies

Two series of novel platinum(II) 2,6‐bis(1‐alkylpyrazol‐3‐yl)pyridyl (N5Cn) complexes, [Pt(N5Cn)Cl][X] ( 1 – 9 ) and [Pt(N5Cn)(C?CR)][X] ( 10 – 13 ) (X=trifluoromethanesulfonate (OTf) or PF₆; R=C₆H₅, C₆H₄‐p‐CF₃ and C₆H₄‐p‐N(C₆H₅)₂), with various chain lengths of the alkyl groups on the nitrogen atom of the pyrazolyl units have been successfully synthesized and characterized. Their electrochemical and photophysical properties have been studied. Some of their molecular structures have also been determined by X‐ray crystallography. Two amphiphilic platinum(II) 2,6‐bis(1‐tetradecylpyrazol‐3‐yl)pyridyl (N5C14) complexes, [Pt(N5C14)Cl]PF₆ ( 7 ) and [Pt(N5C14)(C?CC₆H₅)]PF₆ ( 13 ), were found to form stable and reproducible Langmuir–Blodgett (LB) films at the air–water interface. The characterization of such LB films has been investigated by the study of their surface pressure–area (π–A) isotherms, UV/Vis spectroscopy, XRD, X‐ray photoelectron spectroscopy (XPS), FTIR, and polarized IR spectroscopy. The luminescence property of 13 in LB films has also been studied.     

Electrochemical Properties of Electrode Modified with Langmuir‐Blodgett Film of p‐tert‐Butylcalix[4]arene Derivatives and Its Application in Determining of Silver

A new type of voltammetric sensor, Langmuir‐Blodgett (LB) film of 5,11,17,23‐tetra‐tert‐butyl‐25,27‐di(3‐thiadiazole‐propanoxy)‐26,28‐dihydroxycalix[4]arene modified glassy carbon electrode (LB_TZCA–GCE), was prepared. The electrochemical properties of LB_TZCA–GCE were researched in detail and its recognizing mechanism for silver ion in aqueous solution was discussed. Using this voltammetric sensor, a new stripping voltammetric method for determining of Ag⁺ was erected with good sensitivity, selectivity, reproducibility and recovery. The detection limit was 8×10^?9 M at accumulation time of 180 s. By this method, real samples (lake water, tap water and synthesis sample) were analyzed and the results obtained were well satisfactory.     

Preparation and characterization of 5,10,15,20‐tetraphenylporphyrin Langmuir films for gas chemsensor applications

In this work is reported the preparation and characterization of 5,10,15,20‐tetraphenylporphyrin (H₂TPP) films at the water‐air interfaces. The surface pressure‐area isotherms (π‐A) and UV‐Vis spectroscopy were used to investigate the effect of the spreading methods and parameters on the porphyrin monolayer formation. Also, Langmuir‐Blodgett (LB) and Langmuir‐Schaefer (LS) films were deposited onto glass substrates in order to study the conformation changes in porphyrin molecular packing. Quartz crystal microbalance (QCM) was utilized as the active solid substrate for the development of the NO₂ gas sensor based on the H₂TPP molecular films. The results of π‐A curves have clearly shown the significant contribution of the preparation methods and processing parameters on the conformation of porphyrin molecular films. The UV‐Vis spectroscopy results using polarized absorption dichroism have indicated different molecular packing for porphyrin films deposited by LB and LS methods, with relative tilted angles of 50° ± 5° and 35° ± 5°, respectively. Moreover, the QCM response has given strong evidence that H₂TPP porphyrin molecular films have performed as NO₂ chemsensor. Copyright © 2011 John Wiley & Sons, Ltd.     

Structural polymorphism in poly(dodecamethylen‐di‐O‐methyl‐L‐tartaramide)

Structural characterization of poly(dodecamethylen‐di‐O‐methyl‐L‐tartaramide) was carried out with optical microscopy, thermal analysis, X‐ray diffraction, and electron microscopy. Two different crystalline forms were found in accordance with the thermograms, powder and fiber X‐ray diffraction diagrams. The electron microscopy allows corroboration of the morphological and crystallographic differences. Molecular modeling was used to conclude the structural analogies and differences between the two crystalline forms that were related to the chain packing and orientation in the crystal cell, respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2523–2530, 2002     

Surface morphology of Ge‐modified 3C‐SiC/Si films

The influence of Ge deposition prior to carbon interaction with 3° off‐axis Si(111) substrates on the structural and morphological properties of the formed silicon carbide (SiC) layer is studied. In situ reflection high‐energy electron diffraction (RHEED) and X‐ray diffraction (XRD) revealed the formation of the cubic silicon carbide (3C‐SiC) modification. In situ spectroscopic ellipsometry measurements revealed a decreasing 3C‐SiC thickness with increasing Ge predeposition. Atomic force microscopy (AFM) studies revealed that the surface overlayer morphology is mainly formed by periodic step arrangements whose relevant geometric parameters, i.e. lateral separation, height and terrace width, depend on the Ge content. Besides the changes of the step morphology, the surface roughness and the grain size and the strain of the formed 3C‐SiC decreases with increasing germanium precoverage. Copyright © 2008 John Wiley & Sons, Ltd.     

Filling‐level effect on the physical properties of MgBr2‐ and MgCl2‐filled poly(vinyl acetate) films

The structural properties of poly(vinyl acetate) (PVAc) films filled with different levels of MgBr₂ or MgCl₂ were investigated. Differential scanning calorimetry revealed that, at certain filling levels of MgBr₂ or MgCl₂, two new transitions appeared. The first one was due to the α relaxation (T_α) associated with a crystalline region, and the second was due to the melting temperature (T_m). This implies that a crystalline phase was formed in the polymeric matrix. Changes occurring in T_α, T_m, and the melting peak area as a function of the filling level were examined. The X‐ray diffraction (XRD) pattern revealed that the pure PVAc film was amorphous. However, the addition of MgBr₂ or MgCl₂ led to the formation of a crystalline phase in the polymeric matrix that depended on the filling level. XRD also demonstrated that the structural changes depended not only on the metal ions but also on the halide ions. Scanning electron microscopy images for the studied samples were examined. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 112–119, 2003     

Crystallisation of aspirin via simulated pulmonary surfactant monolayers and lung‐specific additives

Pain is a prevalent condition that can have a serious impact upon the socioeconomic function of a population. Numerous methods exist to administer analgesic medication (e.g. aspirin) to the body however inherent drawbacks limit patient acceptability. The inhaled route offers promise to facilitate the administration of medication to the body. Here, we consider the crystallisation behaviour of aspirin, our model therapeutic agent, when in contact with material of relevance to the lung. Thus, our approach aims to better understand the interaction between drug substances and the respiratory tract. Langmuir monolayers composed of a mixed surfactant system were supported on an aqueous subphase containing aspirin (7.5 mg/ml). The surfactant film was compressed to either 5mN/m (i.e. inhalation end point) or 50 mN/m (i.e. exhalation end point), whilst located within a humid environment for 16 h. Standard cooling crystallisation procedures were employed to produce control samples. Antisolvent crystallisation in the presence or absence of lung‐specific additives was conducted. All samples were analysed via scanning electron microscopy and X‐ray diffraction. Drug‐surfactant interactions were confirmed via condensed Langmuir isotherms. Scanning electron microscopy analysis revealed plate‐like morphology. The crystallisation route dictated both the crystal habit and particle size distribution. Dominant reflections were the (100) and (200) aspects. The main modes of interaction were hydrogen bonding, hydrophobic associations, and van der Waals forces. Here, we have demonstrated the potential of antisolvent crystallisation with lung‐specific additives to achieve control over drug crystal morphology. The approach taken can be applied in respirable formulation engineering. Copyright © 2017 John Wiley & Sons, Ltd.     

Preparation and characterization of redox cellulose Langmuir–Blodgett films containing a ferrocene derivative

The 3‐ferrocenoylpropanoyl group, one of the redox species, was introduced at C‐2 and/or C‐3 positions of 6‐O‐(4‐stearyloxytrityl)cellulose. The spreading behavior of the cellulose derivatives on the water surface and the properties of Langmuir–Blodgett (LB) films were investigated. The surface pressure–area isotherm of the cellulose monolayer was changed by the subphase temperature. Uniform monolayers of 6‐O‐(4‐stearyloxytrityl)cellulose 3‐ferrocene propionate (STCFc) could be deposited successively onto several substrates by the horizontal lifting method at 10 mN m^?1, and this produced X‐type LB films. The successive uniform depositions of STCFc were confirmed by ultraviolet–visible absorption spectra. X‐ray diffraction measurements indicated that the thickness of the STCFc molecules in the LB films was 1.99 nm. Fourier transform infrared spectroscopy measurements supported the idea that hydrocarbon chains in the LB films were highly ordered (trans‐zigzag) and oriented considerably perpendicular to the surface of the substrate. Moreover, the C?O group of the ferrocenoyl groups was perpendicular to the surface of the substrate, and the ferrocene group was occupied in the water phase. Cyclic voltammograms for the STCFc monolayer on a gold electrode exhibited surface waves. The interfacial electron‐transfer process between the redox site incorporated into the cellulose LB monolayer and the electrode surface was fast enough at a scanning rate lower than 100 mV s^?1. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5023–5031, 2005     

Controlling the Structural and Electrical Properties of Diacid Oligo(Phenylene Ethynylene) Langmuir–Blodgett Films

The preparation, characterization and electrical properties of Langmuir–Blodgett (LB) films composed of a symmetrically substituted oligomeric phenylene ethynylene derivative, namely, 4,4′‐[1,4‐phenylenebis(ethyne‐2,1‐diyl)]dibenzoic acid (OPE2A), are described. Analysis of the surface pressure versus area per molecule isotherms and Brewster angle microscopy reveal that good‐quality Langmuir (L) films can be formed both on pure water and a basic subphase. Monolayer L films were transferred onto solid substrates with a transfer ratio of unity to obtain LB films. Both L and LB films prepared on or from a pure water subphase show a red shift in the UV/Vis spectrum of about 14 nm, in contrast to L and LB films prepared from a basic subphase, which show a hypsochromic shift of 15 nm. This result, together with X‐ray photoelectron spectroscopic and quartz crystal microbalance experiments, conclusively demonstrate formation of one‐layer LB films in which OPE2A molecules are chemisorbed onto gold substrates and consequently ? COO? Au junctions are formed. In LB films prepared on a basic subphase the other terminal acid group is also deprotonated and associates with an Na⁺ counterion. In contrast, LB films prepared from a pure water subphase preserve the protonated acid group, and lateral H‐bonds with neighbouring molecules give rise to a supramolecular structure. STM‐based conductance studies revealed that films prepared from a basic subphase are more conductive than the analogous films prepared from pure water, and the electrical conductance of the deprotonated films also coincides more closely with single‐molecule conductance measurements. This result was interpreted not only in terms of better electron transmission in ? COO? Au molecular junctions, but also in terms of the presence of lateral H‐bonds in the films formed from pure water, which lead to reduced conductance of the molecular junctions.