Design of thermochromic polymer blends containing low‐mass compounds

We investigated the light transmittance of an immiscible polymer blend comprising a copolymer of ethylene and vinyl acetate (EVA) and a terpolymer of vinyl butyral, vinyl alcohol, and vinyl acetate (PVB). Both EVA and PVB are used in the interlayers of laminated glass. We found that the transparency of the blend depends on the ambient temperature. This can be attributed to the difference in the temperature dependence of the refractive index between EVA and PVB. The blend has good transparency at room temperature because the difference between the refractive indices of its components is minimal. At high or low temperatures, however, the blend becomes opaque owing to light scattering. The addition of a plasticizer favorably affects the temperature range over which the blend exhibits high transparency, because the refractive index and its temperature dependence are affected by the plasticizer. We also evaluated the interphase transfer of a plasticizer between EVA and PVB at various temperatures. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45927.     

Polymers bearing intramolecular photodimerizable probes for mass diffusion measurements by the forced Rayleigh scattering technique: synthesis and characterization

A new photochromic probe, bis(9-anthryl methyl) ether (BAME) derivative, was synthesized and introduced as an effective probe for forced Rayleigh scattering (FRS) measurement. It is shown that BAME and polystyrene labelled with BAME exhibit a large change in refractive index under irradiation of u.v. light (363.8 nm). The self-diffusion of BAME and polystyrene labelled with BAME (PSA) were measured in various solvents. Results of PSA in good, marginal and poor solvents are consistent with those obtained from quasi-elastic light scattering (QELS). Since the photodimerization reaction of anthracene has been extensively studied in solution and crystal as well as in polymer matrix, unfavourable multistep photochemical reactions can be avoided. One such unfavourable case, which involves a fluorescence quenching solvent CCl₄, is demonstrated. A temperature dependence study of polystyrene in semi-dilute theta solution by FRS has suggested that the non-exponential intensity decay is due to large concentration fluctuations in the solution. The well known photochemistry, large refractive index change and temperature stability have made BAME a very promising probe for FRS measurements.     

TRANSPARENTE POLYMERE MEHRPHASENSYSTEME

Usually two phase polymer blends are not transparent because of differences in the refractive indices of their components and the resulting light scattering. By means of model calculations on the basis of the Mie-theory, the conditions for transparency in two-phase polymer blends are investigated. The models used are homogeneous spheres or spheres with a core-shell morphology imbedded in the polymer matrix. The light scattering of these particles is calculated as a function of diameter, refractive index, wavelength and particlecomposition. Results are presented that show the limits of diameter and difference in the refractive indices between matrix and particle for homogeneous particles to obtain transparency. In the case of large differences in the refractive indices or of large diameters the use of spheres with a core-shell morphology is favourable. Depending on the refractive indices of the respective phases, there exists an optimal composition of these spheres to obtain transparent polymer-blends. Another way to transparency is the minimization of light scattering by interparticle interferences, which can be achieved by special types of block-copolymers.     

The optical properties of two-phase polymer systems: Single scattering in monodisperse,non-absorbing systems

Two-phase polymer systems have achieved commercial importance due mainly to the improvement in impact strength brought about by the addition of dispersed rubber particles to a normally brittle glassy polymer. Rubber-reinforced polystyrene and ABS plastics are two familiar examples. An important drawback of this class of materials is their lack of transparency, caused by the scattering of light at the interface between the phases. The theory of light scattering by spherical particles indicates that the degree of scattering (turbidity) is a function of the amount of dispersed phase present, its particle size, the ratio of refractive indices of the phases, and the wavelength of light. Quantitative predictions of the effects of the above parameters on the transparency of two-phase systems can be made, providing answers to the questions “How close must the refractive indices be?” and “What size must the dispersed-phase particles be?” for a given level of transparency. Calculations for typical polymer pairs reveal that at a given dispersed-phase level, a maximum in turbidity is obtained roughly in the range of particle sizes thought to be necessary for good impact strength. Also, if the refractive indices are matched at a particular temperature, small particle sizes greatly increase the temperature range over which scattering is minimized.     

Characterization of styrene-butadiene copolymers by light scattering

The general theory of Stockmayer and Benoit and their coworkers yields the weight average molecular weight of a binary copolymer and parameters which reflect the heterogeneity of chemical composition of the copolymer, using light scattering data from solutions in at least three solvents with different refractive indices. Although this theory has been applied successfully to block and graft copolymers and to mixtures of homopolymers, it has not seemed to be valid for random copolymers.In this report, molecular weight and heterogeneity parameters of a number of gel-free styrene-butadiene emulsion copolymers were estimated from results of light scattering measurements in toluene, cyclohexane and 1,2-dichloroethane. The calculated heterogeneity parameters contradict expectations from copolymerization theory and appear to be in error. It is suggested that the particular difficulties with statistical copolymers result from a dependence of specific refractive index increment on polymer molecular weight. This dependence varies with different solvents. The effect is illustrated by experimental results for polystyrenes in toluene, cyclohexane and 1,2-dichloroethane. Accurate study of copolymer characteristics requires selection of solvents such that the differences between specific refractive indices of the appropriate homopolymer solutions do not depend strongly on polymer molecular weight in the molecular weight range which corresponds to the sum of homopolymer sequences in the particular copolymers. The apparent inapplicability of the theory to random copolymers appears to be an artifact of the particular systems which were studied.     

Light losses in sol-gel coatings

It is shown that the translucence of a substrate strongly influences light transmission by glass articles modified by sol-gel coatings. In contrast to glass, where light scattering is proportional to the refractive index, an inverse proportionality has been found in the films studied, which can be explained by the influence of porosity on the decrease of the refractive index of the coating.     

Truths and myths about the determination of molar mass distribution of synthetic and natural polymers by size exclusion chromatography

This article discusses various aspects of the determination of molar mass distribution by means of size exclusion chromatography (SEC) in various application modes. The effects of erroneous specific refractive index increment (dn/dc), branching, column performance, and enthalpic interactions on the results obtained by different SEC techniques are discussed. Combination of SEC and a light scattering detector represents the most direct way to the molar mass distribution of all natural and synthetic polymers as it completely eliminates the need for column calibration and to a certain extent eliminates the dependence of the obtained results on some operational variables such as flow rate, temperature, or injected mass. A multiangle light scattering (MALS) photometer has become the most frequently used light scattering detector capable of determination of molecular size as another important polymer characteristic. This article contrasts SEC‐MALS method with other application modes of SEC from the viewpoint of some frequent confusions and misunderstandings. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40111.     

Effects of composition and plastifier on the light scattering of polymer glasses and properties of polymeric optical fibers made from styrene-methyl methacrylate copolymers

High optical purity polystyrene (PS), poly(methyl methacrylate) (PMMA) and styrene-methyl methacrylate statistical copolymers (S-MMA) were prepared. Light scattering measured on polymeric glasses depends on the chemical composition of the polymer and on the refractive index of the plastifier added. An isorefractive plastifier reduces considerably the scattering values for the copolymers S-MMA, while having no significant effect on the scattering of PMMA. A plastifier with a refractive index different from that of the polymer raises distinctly the light scattering values in all cases. It has been shown that the isorefractive plastifier has a favourable effect on attenuation loss of polymeric optical fibers (POF) obtained from the copolymer S-MMA 2/1.     

A light scattering study of some solutions of triblock copolymers

Three samples of polystyrene-polybutadiene-polystyrene block copolymers have been studied by means of the light scattering technique in several solvents. The light scattering measurements indicate the degree of heterogeneity of the samples. Further measurements which were made on the least heterogeneous of the samples in a solvent closely matching the refractive index of the centre block suggest that the two types of polymer are largely separate. In this case the angular intensity variation of the light scattering can be interpreted in terms of the scattering obtained from a “dumb-bell” configuration.     

Electro-optic properties of liquid suspension of pbTio3 ultrafine powders

polar PbTio₃ ultrafine powders derived form Sol-Gel process is suspended in many liquid mediums by ultrasonic wave. In this paper, electric field-induced light transmission and scattering of PbTiO₃ ultrafine powder suspension has been investigated. The effect of powder shapes, radius of powders, concentration of suspension and dispersion medium on light scattering and transmission is reported. The change of transmission light reaches 100, while for the scattering light reaches 30%. Electric field-induced change of refractive index of PbTiO₃ powder suspensions has also been observed.     

Additive and free-volume effects on the refractive index of a thiol-ene polymer network

A series of hard, transparent, thermoset polymer samples containing tetravinylsilane (TVS) and 1,3-benzenedithiol (BDT) with varying loadings of zirconium oxide clusters Zr₆(OH)₄O₄(OMc)₁₂ (ZOC) were synthesized. Resulting polymers exhibited a higher refractive index (n) than the parent polymer containing only the monomers TVS and BDT. The refractive index reached a maximum value of 1.711 at a ZOC loading of 3 wt% and then decreased as the ZOC concentration in the polymer matrix increased. The refractive index of ZOC was determined to be 1.540 using the Becke line method. Because the refractive index of ZOC is lower than that of the TVS–BDT polymer matrix, the finding that the incorporation of small quantities of ZOC can increase the refractive index of the TVS–BDT polymer composite was unexpected and is accounted for by the effects of ZOC on the packing efficiency of the composite.     

Photobleaching for the formation of nonlinear optical polymer waveguide devices

A simple but realistic kinetic model has been developed to delineate the refractive index profiles formed by photochemical reaction in nonlinear optical polymers. The effects of the absorption due to the unconverted reactant and the photoproduct are included in the model. The parameters required in the model are obtained from simple transmission experiments. The experimental results are consistent with the model. The refractive index profile is steeper when nonlinear optical polymeric materials are bleached by light with higher absorption. The rate of the bleach depth change becomes slower as the bleaching proceeds. Small absorption of bleaching light due to the photoproduct has significant effect on the resulting refractive index profiles. The photobleaching process is shown to be accelerated by the addition of a photosensitizer. Photobleaching time has been effectively reduced by a factor of 3–5. Linear and nonlinear optical properties of the polymer were little affected by the addition of the photosensitizer. It has also been demonstrated that the photobleaching technique can be utilized to tune the initial state of a directional coupler switch after completing the fabrication of the device. It was shown that successive cross states are passed from the initial cross state by selective bleaching of the gap region. The evolution of the refractive index profiles is successfully applied to predict the evolution of output state.     

A LASER INTERFEROMETER FOR MONITORING THIN FILM PROCESSES: APPLICATION TO POLYMER DISSOLUTION

An instrument has been assembled which is well suited for monitoring changes in transparent films and coatings where the thickness ranges from several μm down to fractions of a μm. The operation is based on thin film optical interferometry. Applications include measurement of the dissolution rate in selected organic solvents of a 2-μm thick film of poly(methyl methacrylate) (PMMA) which has been coated on a silicon-oxide-surfaced silicon wafer. Such measurements are often required in developing images from electron-beam or X-ray exposure in microlithography and microelectronics. An unpolarized light beam from a 2 mW He-Ne laser is directed obliquely onto the surface of the film. From the time dependence of the intensity of reflected light, both the rate of dissolution and the refractive index of the film can be ascertained. A review of the optical theory upon which such measurements are based is included. The scope of additional information obtainable through application of this technique, including assessment of the optical integrity of polymer/liquid boundaries during dissolution, is also discussed.     

Obtaining antireflecting coatings from mesoporous silicon dioxide on silicate glass at lowered temperatures of baking of gel

Silicon dioxide sol with oligoethers can be used to obtain antireflecting coatings on silicate glass at various baking temperatures of the coating: 400, 300, and 200°C. At an optimal concentration of 4.0 mass % of oligoether based on PPG-725 in a sol, the maximum light transmission of 99.7%, and the refractive index of the nanoporous coating of 1.23 do not depend on the baking temperature in the range from 200 to 400°C. Silicon dioxide sol with a 4.0 mass % of ALM-10 give a maximum light transmission of 99.7% and a refractive index of the nanoporous coating of 1.23 at a baking temperature of 300–400°C. A maximum light transmission of the glass with a coating of 98.7% and the refractive index of 1.27 at an optimal concentration of 8.0 mass % of oligoether based on PEG-200 were obtained at baking temperatures of 300–400°C.     

Experimental Evaluation of the Optical Properties of Porous Silica/Carbon Composite Particles

Light scattering by porous spheroidal silica and several silica/carbon composite particles having different carbon contents was systematically investigated using a laser particle counter coupled with a pulse height analyzer (LPC-PHA). A new and simple method for the measurements of the effective complex refractive index of silica/carbon composite particles using a conventional LPC-PHA system and a differential mobility analyzer was introduced and tested. Challenge particles, from pure silica to silica/carbon compounds having a gradually increasing porous structure, were prepared by spray-drying methods for use in testing of the inversion method. By representing the deviation of the real part of the refractive index of a porous silica particle versus the size on a topographical map, the inversion method for the determination of the real part of the refractive indices was found to have a satisfactory precision. Furthermore, the method can be applied to the measurement of the complex refractive index of silica/carbon composite particles by extending the best fitting method to complex refractive indices. The effective complex refractive index of silica/carbon composite particles as a function of their carbon content is reported. Both the real and imaginary parts of the complex refractive index were increased with increasing carbon content of the composite particles.     

Bistable light scattering effects in a (side chain liquid crystalline polymer)/(low molecular weight liquid crystal) composite and in a ferroelectric liquid crystalline polymer

The electro-optical effects and aggregation states of liquid crystalline polymer (LCP)/ low molecular weight liquid crystal (LC) composite and ferroelectric liquid crystalline copolymer (FLCP) have been investigated. The nematic LCP was observed to be miscible with the nematic LC over wide ranges of concentration and temperature. The binary mixture showed an induced smectic phase in the range of 80/20-20/80 mol%. The electro-optical effects of the LCP/LC composite in an induced smectic phase could be classified into the turbid (light- scattering) and the transparent states upon application of AC and DC electric fields, respectively. The transient scattering mode was obtained by repeated voltage polarity reversal in the chiral smectic C phase of FLCP. The reversible transparent-opaque (light scattering) change was observed in the chiral smectic C state upon application of DC and AC electric fields, respectively. Both transparent and light-scattering states of the LCP/LC composite and the FLCP could be maintained, even after the electric field had been turned off (memory effect). The bistable effects of LCP/LC composite and FLCP are opposite under the same conditions. A novel type of electro-optical effect on light scattering was obtained for liquid crystalline polymer in the smectic states.     

Drying dynamics of polymers films by an interferometric technique

We analyze a simple laser reflectivity measurement as a tool to monitor the drying kinetics of transparent polymer films. The reflectivity signal of a laser beam at normal incidence shows oscillations due to interference arising from multiple reflection of the laser light within the drying film. We develop a model to interpret the reflectivity curves in terms of time evolving refractive indices at the top and bottom of the film. We present results of the drying kinetics of transparent alkyd films on a glass substrate of high refractive index. Data shows a clear hallmark indicating the evolution of the crosslinking process. From the reflectivity curves, the time evolution of the refractive indices at the top and bottom is obtained. Assuming a linear-gradient of the refractive index along the depth of the film the average refractive index and consequently the film thickness as a function of time are estimated. Clear features in the time evolution of the refractive indices and thickness, correlate well with qualitative “dust”, “touch” and “fingerprint” drying times. Additionally, we present some preliminary results for water based latex binders, where scattering of light is present, showing that this simple optical technique could be extended for studying latex film formation.     

Preparation of acrylate polymer/silica nanocomposite particles with high silica encapsulation efficiency via miniemulsion polymerization

Acrylate polymer/silica nanocomposite particles were prepared through miniemulsion polymerization by using methyl methacrylate/butyl acrylate mixture containing the well-dispersed nano-sized silica particles coupling treated with 3-(trimethoxysilyl)propyl methacrylate (MPS). The encapsulation efficiency of silica particles was determined through the elution and hydrofluoride acid etching experiments, and the size distribution and the morphology of the composite latex particles were characterized by dynamic light scattering and transmission electron microscopy. The coupling treatment of silica with MPS can improve the encapsulation efficiency of silica and the degree of grafting of polymer onto silica. When 0.10 g MPS/g silica was used to modify silica, the encapsulation efficiency of silica was greater than 95%, and the degree of grafting of acrylate polymer onto silica was about 60%. Although the average size and the size distribution index of the composite latex particles increased as the weight fraction of silica increased, the stable latex containing the ‘guava-like’ composite particles was obtained. The grafting of polymer onto silica particles improved the dispersion of silica particles in the solvents for acrylate polymer and in the polymer matrix.     

Photocontrol of the refractive index of poly(methyl methacrylate) with a nitrone additive

Hydroxy‐substituted aromatic nitrone derivatives were used for the photochemical control of the refractive index of poly(methyl methacrylate) (PMMA) films. Upon irradiation with 366‐nm light in solution, these derivatives underwent rearrangement reactions, which eventually produced N,N‐diarylformamide derivatives in quantitative yields. Similar photoreactions of the aromatic nitrones in the PMMA films lowered the refractive index of the films by as much as 0.014. The magnitude of the observed refractive‐index change was enough for hydroxy‐substituted nitrones to be used as additives for the fabrication of graded‐index‐type polymer optical fibers. In addition, the refractive index of the PMMA films remained almost constant at any conversion of the starting nitrone derivatives for at least 70 days at room temperature. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2517–2520, 2004     

Static measurements of refractive index increments at 633 nm with a modified refractive index detector

Summary A R 401 Waters Assoc. differential refractometer has been modified to obtain the variation of refractive index increments, dn/dc, of polymer solutions at 633 nm. The introduced modifications were in the sample injection system and in the light source. The performance of the modified refractometer both with aqueous and organic solutions is analyzed. In order to localize a conformational transition in lysozyme, the dependence of dn/dc on temperature for lysozyme solutions in phosphate buffer is studied. Similarly, (dn/dc)_k values for the ternary n-alkane/butanone/poly(dimethyl siloxane) systems over the whole composition range of the binary solvent mixtures are evaluated.