Elastic excitations in polycarbonate membranes

Brillouin light scattering was used to probe acoustic waves propagating with both longitudinal and transverse polarizations in the surface and the bulk of self‐supported particle track‐etched polycarbonate membranes with 15‐ and 80‐nm nanopores. The recorded scattering line shape at gigahertz frequencies reveals changes in the surface waves of the membranes which are more pronounced for the 80‐nm nanopores despite the low porosity (0.7 and 0.05%). Because the measured elastic constants (1.2 and 6.2 GPa) were found to compare very well with the values for thick polycarbonate film, modifications of the elasto‐optical coefficients and/or the transparency might be the reason for the different scattering line shapes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3311–3317, 2004     

Preparation and characterization of chiral polyacrylates end‐capped with bornyl groups in the side chains

Chiral polyacrylates with bornyl end‐capped side chains with four kinds of mesogenic moieties (azobenzene, biphenyl, benzoyloxy biphenyl, and phenyl benzoate) were prepared. The phase properties of the polymers were investigated with X‐ray diffraction, differential scanning calorimetry, and polarizing optical microscopy. The thermogravimetric characteristics, the glass‐transition temperatures and weight‐average molecular weights, of the homopolymers were evaluated. The optical properties of the synthesized polymers in diluted solutions and in the thin‐film state were also evaluated. The optical behavior of the composite films upon photoirradiation was investigated through the change in the transmittance of the probe light triggered by ultraviolet (365‐nm) irradiation. Ultraviolet irradiation and heat treatment caused a reversible intensity change of the probe light at λ = 400 nm. The shrinkage of the photoisomerization of the composite films was also investigated with atomic force microscopy. A spot contraction appeared on the surface when it was irradiated with a laser light spot. The contraction was recovered by heat treatment at 80 °C for 10 min. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1075–1092, 2004     

Covalent Self‐Assembly and One‐Step Photocrosslinking of Tyrosine‐Rich Oligopeptides to Form Diverse Nanostructures

We present covalently self‐assembled peptide hollow nanocapsule and peptide lamella. These biomimetic dityrosine peptide nanostructures are synthesized by one‐step photopolymerization of a tyrosine‐rich short peptide without the aid of a template. This simple approach offers direct synthesis of fluorescent peptide nanocages and free‐standing thin films. The simple crosslinked peptide lamella films provide robust mechanical properties with an elastic modulus of approximately 30 GPa and a hardness of 740 MPa. These nanostructures also allow for the design of peptidosomes. The approach taken here represents a rare example of covalent self‐assembly of short peptides into nano‐objects, which may be useful as microcompartments and separation membranes.     

Optically induced birefringence and holography in silk

In this study, we demonstrated that thin films of azobenzene‐modified Bombyx mori silk showed optically induced effects similar to those found in other polymers incorporating azobenzene moieties. Optically induced anisotropy in refractive index reached 7 × 10^?3 with 18 J cm^?2 required to reach 50% of steady state. Holograms were formed with diffraction efficiencies reaching 2.5%. The holograms were accompanied by surface relief gratings and measurements of the mechanical properties of films with surface relief gratings showed that the raised areas were more adhesive than the lower areas. We also demonstrated the fidelity of holographic images. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Constant loss in Brillouin spectra of polymers

The polarized (VV) and depolarized (VH) light scattering spectra of polyisobutylene, poly(methyl methacrylate), and glycerol were measured in the gigahertz frequency range at temperatures below and above the glass transition. Both VV and VH spectra exhibit a significant constant loss contribution that appears as a frequency‐independent imaginary part of the susceptibility spectrum. Existence of the frequency‐independent susceptibility in VV spectra below the Brillouin lines suggests that the constant loss also appears in mechanical relaxation in the gigahertz frequency range. Intensity of the constant loss increases strongly with temperature. Analysis of the spectra and literature data suggests that the constant loss can be general for many glass‐forming systems, but it is hidden in many cases by other relaxation contributions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 201–209, 2002     

Effect of adjacent hydrophilic polymer thin films on physical aging and residual stress in thin films of poly(butylnorbornene‐ran‐hydroxyhexafluoroisopropyl norbornene)

The properties of thin supported polymer films can be dramatically impacted by the substrate upon which it resides. A simple way to alter the properties of the substrate (chemistry, rigidity, dynamics) is by coating it with an immiscible polymer. Here, we describe how ultrathin (ca. 2 nm) hydrophilic polymer layers of poly(acrylic acid) and poly(styrene sulfonate) (PSS) impact the aging behavior and the residual stress in thin films of poly(butylnorbornene‐ran‐hydroxyhexafluoroisopropyl norbornene) (BuNB‐r‐HFANB). The aging rate decreases as the film thickness (h) is decreased, but the extent of this change depends on the adjacent layer. Even for the thickest films (h > 500 nm), there is a decrease in the aging rate at 100 °C when BuNB‐r‐HFANB is in contact with PSS. In an effort to understand the origins of these differences in the aging behavior, the elastic modulus and residual stress (σ_R) in the films were determined by wrinkling as a function of aging time. The change in the elastic modulus during aging does not appear to be directly correlated with the densification or expansion of the films, but the aging rates appear to roughly scale as hσ_R^1/3. These results illustrate that the physical aging of thin polymer films can be altered by adjacent polymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 992–1000     

Chemically Delaminated Free‐Standing Ultrathin Covalent Organic Nanosheets

Covalent organic nanosheets (CONs) are a new class of porous thin two‐dimensional (2D) nanostructures that can be easily designed and functionalized and could be useful for separation applications. Poor dispersion, layer restacking, and difficult postsynthetic modifications are the major hurdles that need to be overcome to fabricate scalable CON thin films. Herein, we present a unique approach for the chemical exfoliation of an anthracene‐based covalent organic framework (COF) to N‐hexylmaleimide‐functionalized CONs, to yield centimeter‐sized free‐standing thin films through layer‐by‐layer CON assembly at the air–water interface. The thin‐layer fabrication technique presented here is simple, scalable, and does not require any surfactants or stabilizing agents.     

Luminescence of monolayer thin films of the fully conjugated rigid‐rod polymer poly(p‐phenylenebenzobisthiazole)

Poly(p‐phenylenebenzobisthiazole) (PBT) is a heterocyclic, aromatic rigid‐rod polymer with a fully conjugated backbone and excellent dimensional, thermo‐oxidative, and solvent stabilities. A PBT polymer with an intrinsic viscosity of 18.0 dL/g was dissolved in methanesulfonic acid or Lewis acid. The PBT solution was spin‐coated and doctor‐bladed for freestanding films or onto an indium tin oxide (ITO) substrate. The acid was removed via coagulation. Scanning electron microscopy determined that the resultant film thicknesses were about 340 and 60 nm for PBT freestanding films and films on the ITO substrate, respectively. X‐ray scattering demonstrated that the freestanding films were in‐plane isotropic without long‐range order. The freestanding films were excited with a He‐Cd laser at 325 nm for photoluminescence (PL) response. PL spectra showed a distinct intensity maximum at 580 nm, regardless of the film‐forming conditions. After the films cooled to 67 K, the PL maximum shifted to 566 nm with enhanced intensity. Aluminum was evaporated onto the monolayer PBT thin film on the ITO substrate as an electron injector for electroluminescence (EL) response. Diodic electric behavior was observed for all monolayer PBT EL devices for the first time. A threshold voltage as low as 4 V was achieved for the monolayer EL devices. In addition, PBT EL spectra were tunable, with a maximum intensity at 570 nm at a bias voltage of 4.5 V changing to 496 nm at 7.5 V (i.e., a blueshift) with greatly increased intensity. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1760–1767, 2002     

Nanoindentation studies of polyimide thin films with various internal linkages in the diamine component

Polyimide thin films were synthesized from 3,3′,4,4′‐biphenyltetracarboxylic acid dianhydride (BPDA) and four different diamines (p‐phenylene diamine, 4,4′‐oxydiphenylene diamine, 4,4′‐biphenylene diamine, and 4,4′‐sulfonyldiphenylene diamine). The nanoindentation behavior of the resulting polyimides, namely, poly(p‐phenylene biphenyltetracarboximide) (BPDA‐PDA), poly(4,4′‐biphenylene biphenyltetracarboximide) (BPDA‐BZ), poly(4,4′‐oxydiphenylene biphenyltetracarboximide) (BPDA‐ODA), and poly(4,4′‐sulfonyldiphenylene biphenyltetracarboximide) (BPDA‐DDS), were investigated. Also, the morphological properties were characterized with a prism coupler and wide‐angle X‐ray diffraction and were correlated to the nanoindentation studies. The nanoindentation behavior and hardness varied quite significantly, depending on the changes in the chemical and morphological structures. The hardness of the polyimide thin films increased in the following order: BPDA‐DDS < BPDA‐ODA < BPDA‐BZ < BPDA‐PDA. For all the polyimide thin films, except that of BPDA‐BZ, the hardness decreased with an increase in the load. The birefringence, a measure of the molecular in‐plane orientation, increased in the following order: BPDA‐DDS < BPDA‐ODA < BPDA‐PDA < BPDA‐BZ. The X‐ray diffraction studies revealed that the crystallinity of the polyimide thin films varied with the changes in the chemical structure. The studies showed that the indentation response with an applied load and the hardness by nanoindentation for the BPDA‐based polyimides were closely related to the morphological structure. The nanoindentation and birefringence results revealed that the mechanical properties of the polyimide thin films were dependent on the crystallinity, which arose because of the chain order along the chain axis and the molecular packing order. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 861–870, 2004     

Stimuli‐responsive buckling mechanics of polymer films

Thin polymer films may undergo a wide variety of elastic instabilities that include global buckling modes, wrinkling and creasing of surfaces, and snapping transitions. Traditionally, these deformations have usually been avoided as they often represent a means of mechanical failure. However, a new trend has emerged in recent years in which buckling mechanics can be harnessed to endow materials with beneficial functions. For many such applications, it is desirable that such deformations happen reversibly and in response to well‐defined signals or changes in their environment. While significant progress has been made on understanding and exploiting each type of deformation in its own right, here we focus on recent advances in the control and application of stimuli‐responsive mechanical instabilities. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1441–1461     

Load and depth sensing indentation as a tool to monitor a gradient in the mechanical properties across a polymer coating: A study of physical and chemical aging effects

Load and depth sensing indentation has been used to characterize the elastic modulus and hardness of various polycarbonate films. This analytical technique is shown to be extremely suitable for the determination of gradients in these mechanical properties. Furthermore, it is demonstrated that such a gradient exists over a length of micrometers in chemically aged polycarbonate, but it is virtually absent in physically aged polycarbonate. From these results, it is concluded that, although the first 100 nm cannot be probed, physical aging occurs homogeneously throughout the bulk of the sample. However, chemical aging starts at the surface and moves progressively into the bulk of the material. From the study of these films, it appears that for the interpretation of these measurements, knowledge about the amount of creep occurring during the measurements and about the mechanical properties of the substrate on which these films are applied is needed. Creep can be measured with the same indenter through the application of a constant load for a period of time. Load and depth sensing indentation appears to be a powerful method for studying the physical and chemical aging of polymers. It is especially valuable for coatings and films for which conventional tensile testing is problematic. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1628–1639, 2004     

Dialdehyde starch‐crosslinked chitosan films and their antimicrobial effects

For improved mechanical and water‐swelling properties of chitosan films, a series of transparent films were prepared with dialdehyde starch as a crosslinking agent. Fourier transform infrared and X‐ray analysis results demonstrated that the formation of Schiff's base disturbed the crystallization of chitosan. The mechanical properties and water‐swelling properties of the films were significantly improved. The best values of the tensile strength and breaking elongation were 113.1 MPa and 27.0%, respectively, when the dialdehyde starch content was 5%. All the crosslinked films still retained obvious antimicrobial effects toward S. aureus and E. coli, and they showed potential for biomedical applications. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 993–997, 2003     

Peeling of polydimethylsiloxane adhesives at low velocities: Cohesive failure

This work presents results obtained in 90‐degree peeling tests at low velocities in the case of Newtonian adhesives, when failure is cohesive. Peeling experiments are described and consider the influence of the thickness, viscosity, and surface tension of the adhesive, as well as the backing rigidity. A simple model, based on lubrication effects in thin films, is considered and compared with the measurements, when peeling is a two‐dimensional phenomenon. Furthermore, a criterion for predicting the transition between the two‐dimensional regime and the three‐dimensional regime at higher velocities is proposed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 145–157, 2005     

Relationship between the polymer/silica interaction and properties of silica composite materials

Cast film composites have been prepared from aqueous polymer solutions containing nanometric silica particles. The polymers were polyvinyl alcohol (PVA), hydroxypropylmethylcellulose (HPMC) and a blend of PVA‐HPMC polymers. In the aqueous dispersions, the polymer–silica interactions were studied through adsorption isotherms. These experiments indicated that HPMC has a high affinity for silica surfaces, and can adsorb at high coverage; conversely, low affinity and low coverage were found in the case of PVA. In the films, the organization of silica particles was investigated through transmission electron microscopy (TEM) and small‐angle neutron scattering (SANS). Both methods showed that the silica particles were well‐dispersed in the HPMC films and aggregated in the PVA films. The mechanical properties of the composite films were evaluated using tensile strength measurements. Both polymers were solid materials, with a high‐elastic modulus (65 MPa for HPMC and 291 for PVA) and a low‐maximum elongation at break (0.15 mm for HPMC and 4.12 mm for PVA). In HPMC films, the presence of silica particles led to an increase in the modulus and a decrease in the stress at break. In PVA films, the modulus decreased but the stress at break increased upon adding silica. Accordingly, the polymer/silica interaction can be used to tune the mechanical properties of such composite films. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1134–1146, 2006     

Preparation and characterization of covalently bonded PVA/Laponite/HAPI nanocomposite multilayer freestanding films by layer‐by‐layer assembly

The layer‐by‐layer (LBL) assembly technique is an attractive method to make functional multilayer thin films and has been applied to fabricate a wide range of materials. LBL materials could improve optical transmittance and mechanical properties if the film components were covalently bonded. Covalently bonded nanocomposite multilayer films were prepared by employing hydrophilic aliphatic polyisocyanate (HAPI) as the reactive component, to react with Laponite and polyvinyl alcohol (PVA). FT‐IR spectra suggested that HAPI reacted with Laponite and PVA at ambient temperature rapidly. Ellipsometry measurement showed that the film thickness was in linear growth. The influences of HAPI on the optical, mechanical and thermal properties of the films were investigated by UV‐Vis spectroscopy, tensile stress measurement, DSC and TGA. The obtained results showed that the optical transmittance and mechanical strength were enhanced when the film components were covalently bonded by HAPI. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 545–551     

Polarization holographic grating recording in the cholesteric azobenzene‐containing films with the phototunable helix pitch

The recording of polarization gratings in films of a cholesteric liquid crystalline polymer with different helix pitch was studied in detail. For this purpose, the cholesteric mixture of the nematic azobenzene‐containing copolymer with a chiral‐photochromic dopant was prepared. The utilization of such mixture has made possible to realize dual optical photorecording in one system, first due to the phototuning of the helix pitch by UV light and second the polarization grating recording process by exposure with polarized visible light. The diffraction efficiency strongly depends on the cholesteric helix pitch and films thickness: the increase of the confinement ratio d/p (where d, film thickness; p, helix pitch) results in growth of the diffraction efficiency. Comparison of the induction of polarization gratings in cholesteric, nematic (copolymer without chiral dopant), and amorphous (nonannealed) cholesteric films revealed that only the cholesteric films were characterized by significant oscillations in the diffraction efficiency signal as well as by the presence of the maximum in the first‐order diffraction efficiency in the initial stage of the grating recording process. It was found that in addition to the polarization grating surface relief gratings (SRGs) were also formed in the studied systems, however, the amplitude of the SRG inscribed in the cholesteric films was lower (～20 nm) compared to the grating amplitude obtained in nematic films (～60 nm). Moreover, increasing helix pitch resulted in a decrease of the SRG amplitude. The obtained experimental data demonstrate the great potential of cholesteric LC mixtures of such type for different applications as photoactive materials for photonics. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 773–781     

Synthesis of novel fluorinated hyperbranched polyimides with excellent optical properties

Novel anhydride‐terminated fluorinated hyperbranched polyimides (FHBPIs) were successfully prepared by condensation of a triamine monomer, 1,3,5‐tris(2‐trifluoromethyl‐4‐aminopheoxy) benzene (TFAPOB), and various aromatic dianhydride monomers with different linear length. UV–vis spectra indicate high optical transparency of FHBPI films with a UV–vis absorption edge of 350–395 nm. FHBPIs show increased mechanical properties with the linear length of dianhydride monomer. Young's moduli of FHBPI range from 2.37 to 2.56 Gpa, similar to those of their linear analogs. These FHBPI films also present a minimum birefringence value as low as 0.0025 at 650 nm and have low optical absorption in the optical communication wavelengths of 1310 and 1550 nm. Rib‐type optical waveguide device fabricated by FHBPI‐4d demonstrated an obvious near‐field mode pattern of the waveguide. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6269–6279, 2009     

Structural evolution of cylindrical‐phase diblock copolymer thin films

We have measured the time evolution of the self‐assembly process in perpendicular‐oriented cylindrical‐phase diblock copolymer thin films using statistical analysis of high‐resolution scanning electron microscope (SEM) images. Within minutes of annealing above the polymer glass‐transition temperature, microphase separation between polymer blocks results in formation of uniform nanometer‐scale domains whose relative position is initially largely uncorrelated. On further annealing, the cylindrical polymer domains organize into a two‐dimensional hexagonal lattice whose characteristic grain size increases slowly with time (～t^1/4). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1970–1975, 2004     

Quantitative characterization of the optical properties of absorbing polymer films: Comparative investigation of the internal reflection intensity analysis method

Nondestructive, three‐dimensional refractive‐index measurements are used for the determination of both the crystallinity and orientation in thin polymer films. The prism wave‐guide coupler is particularly suited for three‐dimensional isotropic and anisotropic thin‐film studies because of the quantitative character of the information obtained and the ease of data acquisition. It has been limited, however, to determining only the refractive index of transparent or weakly absorbing thin‐film samples. On the basis of thin‐film optics, this study develops a new internal reflection intensity analysis (IRIA) method, which uses the intensity information rather than the conventional mode angle values to acquire both the refractive index and the extinction coefficient over a range of transparent to highly absorbing polymer films. Therefore, the IRIA method overcomes the limitations of this prism wave‐guide coupler technique, which can only measure the refractive index of a weakly absorbing sample. With a Metricon PC‐2010 as the skeletal framework, a prototype instrument has been developed to apply and test the IRIA method. A study comparing both the refractive index and extinction coefficient obtained with ellipsometry, ultraviolet–visible/near‐infrared reflectometry, and IRIA for solvent blue 59 dyed polystyrene films confirms that the IRIA method is effective for obtaining the three‐dimensional refractive indices and extinction coefficients of polymer films. In addition, the refractive index and extinction coefficient spectrum (400–800 nm) of solvent blue 59 have been determined with the effective media theory. Furthermore, the three‐dimensional complex refractive indices of highly absorbing black electrical tape, inaccessible to other optical measurement because of its surface character, has been determined by the IRIA method. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 842–855, 2003     

Synthesis and optical properties of novel blue‐light‐emitting poly(p‐phenylene vinylene) derivatives with pendant oxadiazole or cyano groups

Two novel poly(p‐phenylene vinylene) polymers, which carried side substituents with cyano groups or 1,3,4‐oxadiazole, were synthesized by Heck coupling. They consisted of alternating conjugated segments and nonconjugated aliphatic spacers. The polymers had moderate molecular weights, were amorphous, and dissolved readily in tetrahydrofuran and halogenated organic solvents. They were stable up to approximately 340 °C in N₂ and 290 °C in air, and the anaerobic char yield was around 60% at 800 °C. The polymer with cyano side groups emitted blue light in solutions and thin films with identical photoluminescence (PL) maximum at 450 nm; this supported the idea that chain interactions were hindered even in the solid state. The PL maximum of this polymer in thin films was blueshifted upon annealing at 120 °C, indicating a thermochromic effect as a result of conformational changes in the polymer backbone. The polymer containing side substituents with oxadiazole rings emitted blue light in solutions with a PL maximum at 474 nm and blue‐greenish light in thin films with a PL maximum at 511 nm. The PL quantum yields of the polymers in tetrahydrofuran were 0.13–0.24. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1768–1778, 2004