Multiplexed holographic data page storage on a polyvinyl alcohol/acrylamide photopolymer memory

Holographic data pages were multiplexed in different thickness layers of a polyvinyl alcohol/acrylamide photopolymer. This material is formed of acrylamide photopolymers, which are considered interesting materials for recording holographic memories. A liquid crystal device was used to modify the object beam and store the data pages. A peristrophic multiplexing method is used to store a large number of data pages in the same spot in the material. The bit error rate was calculated fitting the histograms of the images to determine what parameters improve the quality of the images.     

Optimization of holographic storage with modulated recording beams in a thick polyvinyl alcohol/acrylamide photopolymer

In a holographic photopolymer system, the storage properties were often limited due to the attenuation in depth of light during the recording step. To obtain smaller values of the depth attenuation profiles in 1 mm thick polyvinyl alcohol/acrylamide (PVA/acrylamide) photopolymers, we used a triangle prism, sitting one face tilted at 13.7 degrees to the axis within the focus of a lens, to modulate the distribution of recording beams. Doing this permitted larger refractive index modulation depth to be achieved, and larger dynamic range (M#=9.2) was obtained in the PVA/acrylamide photopolymers.     

Hologram recording in polyvinyl alcohol/acrylamide photopolymers by means of pulsed laser exposure

The variation in transmittance produced when a photopolymer is irradiated with a pulsed laser is analyzed and experimental results obtained when diffraction gratings are stored using pulsed exposure are presented. In either case, the influence of the energy of the irradiation pulse, the number of pulses, and the pulse repetition rate were studied. The photopolymer used was an acrylamide/polyvinyl alcohol dry film with a yellow eosin-thiethanol-amine mixture as a photoinitiator system. The recording of the gratings was performed by use of a holographic copying process. The samples were exposed and holograms recorded with a collimated beam from a frequency-doubled Nd:YAG (532 nm) Q-switched laser. Our initial results show that it is possible to obtain diffraction gratings with a diffraction efficiency of 60% and a refractive index modulation up to 2.8 x 10(-3). The energetic sensitivities achieved are close to those obtained with the same material and continuous irradiation without a preprocessing of the gratings.     

Self-enhancement of holographic gratings in dichromated gelatin and polyvinyl alcohol films

New experimental results concerning real-time hologram recording in dichromated sensitized gelatin and polyvinyl alcohol are presented. Self-enhancement of the holographic gratings observed in the dark in both of these dye-polymer systems is shown.     

Nonlocal-response diffusion model of holographic recording in photopolymer

The standard one-dimensional diffusion equation is extended to include nonlocal temporal and spatial medium responses. How such nonlocal effects arise in a photopolymer is discussed. It is argued that assuming rapid polymer chain growth, any nonlocal temporal response can be dealt with so that the response can be completely understood in terms of a steady-state nonlocal spatial response. The resulting nonlocal diffusion equation is then solved numerically, in low-harmonic approximation, to describe grating formation. The effects of the diffusion rate, the rate of polymerization, and a new parameter, the nonlocal response length, are examined by using the predictions of the model. By applying the two-wave coupled-wave model, assuming a linear relationship between polymerized concentration and index modulation, the resulting variation of the grating diffraction efficiency is examined.     

Cross talk in holographic memories with lensless phase-conjugate holograms

Recently holographic memory with lensless phase-conjugate holograms has attracted much attention because it opens up the possibility of compact holographic memories. We investigate cross-talk noise in compact holographic memories with angular multiplexing. It turns out that the optimum angular separation is the same as that for the Fourier plane hologram in the leading order and that the noise-to-signal ratio is independent of the positions in the output plane, similar to the case of the image plane hologram.     

纳米羟基磷灰石/聚乙烯醇复合水凝胶的制备和性能研究

通过溶液法首次将纳米羟基磷灰石晶体与聚乙烯醇溶液复合,制备了一系列纳米羟基磷灰石／聚乙烯醇复合水凝胶材料．用TEM、IR、XRD、TG／DTG、DSC和燃烧实验对材料的结构和组成进行了表征,并对复合材料的热稳定性进行了研究。结果表明所制备的n-HA／PVA复合水凝胶材料组成均一,各相比例易于调控。是一种很有前景的生物医用复合材料。     

聚乙烯醇/蒙脱土纳米复合薄膜的制备与性能研究?

以甘油作为增塑剂,经溶液流延法加工制备出 PVA/MMT 纳米复合薄膜,研究了纳米蒙脱土(MMT)对聚乙烯醇(PVA)的改性作用。通过对薄膜的结构表征、力学、光学、吸水性、热稳定性等性能研究表明,DK4型号 MMT 与 PVA 分子有着很好的相容性,添加了不同比例的 MMT 均不同程度提高了薄膜的抗拉强度、热稳定性,降低了薄膜的断裂伸长率、吸水性、水蒸气透过系数、透光率,其中添加了1％ DK4型MMT的PVA薄膜有着最好的改性效果。     

Optical fiber relative-humidity sensor with polyvinyl alcohol film

We describe a fiber-optic relative-humidity (RH) sensor comprising a moisture-sensitive overlay on a single-mode side-polished fiber. The hygroscopic polymeric material deposited was polyvinyl alcohol (PVA), which proved to have good adherence and stability. The film reached a fast equilibrium with atmospheric moisture (in less than 1 min), inducing changes in the output optical power of approximately 10 dB for the 70%-90% RH range. To yield a low-cost device, single-mode standard communication fibers were used; therefore all the components of the sensor can be commercial, mass-produced telecommunication devices. The experimental results obtained are consistent with the expected behavior of the system; the output power decreases because of losses in the polished region of the fiber as the refractive index of its external medium approaches the fiber core value. Because the external medium is PVA film, its refractive index changes in response to its water content.     

Polylactic acid/cellulose whisker nanocomposites modified by polyvinyl alcohol

The aim of this study was to produce biodegradable polylactic acid/cellulose whisker nanocomposites by compounding extrusion and investigate the possibility to use polyvinyl alcohol to improve the dispersion of whiskers in the matrix. Two feeding methods of polyvinyl alcohol and cellulose nanowhiskers were used and evaluated, dry-mixing with polylactic acid prior extrusion or pumping as suspension directly into the extruder. Various microscopic techniques, tensile testing, and dynamic mechanical thermal analysis were used to study the structure and properties of the nanocomposites. Due to immiscibility of the polymers, phase separation occurred with a continuous polylactic acid phase and a discontinuous polyvinyl alcohol phase. The whiskers were primarily located in the polyvinyl alcohol phase and only a negligible amount was located in the polylactic acid phase. This inadequate dispersion of whiskers in the polylactic acid phase was probably the reason why no improvements in thermal properties were seen for the nanocomposites. The relative small improvements in tensile modulus, tensile strength, and elongation to break for the nanocomposites also indicated that it was principally the polyvinyl alcohol phase that was reinforced with whiskers but not the polylactic acid phase.     

一种新型绿敏光致聚合物及全息特性研究

报道了一种新型的对绿光敏感的光致聚合物材料,对环境湿度不敏感,材料的干燥时间短。该材料以丙烯酰胺为单体,N-苯基甘氨酸作为引发剂,藻红B作为光敏剂,并加入成膜剂聚乙烯醇及增塑剂二甲亚砜。对材料中光引发剂、光敏剂及增塑剂浓度进行了优化,发现其有一个最佳值。本材料记录的全息图衍射效率可达50％以上,感光强度为60mJ／cm^2。在光聚物介质上能够记录信噪比比较高的图像,说明该材料可用于全息存储。     

聚乙烯醇/海藻酸钠/碳纳米管复合膜的制备及其吸附性能

通过溶液共混法制备了聚乙烯醇/海藻酸钠/多壁碳纳米管复合膜,对其进行了透光率、力学性能和DSC表征,并研究了对Cr2O27-的吸附性能。结果表明,PVA与SA等质量混合时相容性好;MWNTs的添加有助于提高复合膜力学性能、热性能;在pH值为2、温度为30℃、MWNTs为80mg时,吸附6h后,复合膜对Cr2O27-的去除率达到96.84%。     

Properties of polyvinyl alcohol cement pastes

Properties of cement pastes containing varying amounts of each of polyvinyl alcohol (PVAL), mixtures of polyvinyl alcohol and phenol formaldehyde (PF) and mixtures of poly vinyl alcohol and borax were studied in this paper. Though the strength parameters of the PVAL-cement pastes are comparable to virgin cement paste their resistance to acid is far superior. Soxhlet extraction with water, done to determine leachability of the polymer from the polymer cement paste, revealed that the percentage of polyvinyl alcohol leached out was less when borax or PF resin was added to the PVAL cement paste. The compressive strength of the poly vinyl alcohol–phenol formaldehyde cement paste was found to be inferior to the other two cases but the retention of compressive strength after immersing in each of acid, base and kerosene was much better. In general, polyvinyl alcohol when added to cement pastes improves the chemical resistance properties in terms of retention of compressive strength after exposure to chemicals.     

Holographic characteristics of a 1-mm-thick photopolymer to be used in holographic memories

Poly(vinyl alcohol-acrylamide) photopolymers are materials of interest in the field of digital information storage (holographic memories). We analyzed the behavior of a 1-mm-thick photopolymer. Using a standard holographic setup, we recorded unslanted diffraction gratings. The material has high angular selectivity (0.4 degrees), good sensitivity (88 mJ/cm2), and small losses caused by absorption and scattering of light. It also has a high maximum diffraction efficiency (70%). A significant induction period was seen in the material. The authors hypothesize that, during most of this induction period, polymerization does in fact take place but is not reflected in the appearance of the diffracted light until a certain threshold value of exposure is reached.     

聚乙烯醇/壳聚糖/明胶水凝胶的合成及其对苯酚的吸附研究

以聚乙烯醇(PVA)、壳聚糖和明胶为原料、戊二醛为交联剂,在酸性溶液中通过共混交联反应合成了聚乙烯醇/壳聚糖/明胶水凝胶,单因素法讨论了影响水凝胶性能的因素如:反应物质量比、交联剂用量、反应温度、反应时间等聚乙烯醇/壳聚糖/明胶水凝胶,对不同浓度苯酚溶液的吸附研究.研究结果表明聚乙烯醇/壳聚糖/明胶水凝胶对苯酚有较好的吸附性能.     

Trypsin immobilization on discs of polyvinyl alcohol glutaraldehyde/polyaniline composite

Discs of polyvinyl alcohol cross-linked with glutaraldehyde (PVAG) were synthesized and covered with polyaniline activated with glutaraldehyde (PANIG). Trypsin was covalently immobilized on this composite yielding a preparation containing 21.1 units per disc. The FT-IR spectra of the discs showed bands of PVA (3300 cm^?1, 2930 cm^?1 and 1440 cm^?1) and PANI (1594 cm^?1 and 1100 cm^?1). The best immobilization conditions were: trypsin concentration at 0.2 mg mL^?1, pH 7.6 and 60 min of incubation, similar to polyaniline–trypsin systems reported in the literature. The PVAG–PANIG–trypsin derivative showed an optimal pH and an optimal temperature of 7.0 and 35 °C, respectively. Hydrolysis of casein showed variations in the size of the products, revealing differences between the immobilized enzyme and the mechanism catalyzed by the native enzyme.     

Application of phase-conjugate mirrors during recording of volume holographic memories

We propose, demonstrate, and analyze the application of phase-conjugate mirrors during the recording of volume holographic memories. Our results show that using phase-conjugate mirrors during recording improves the uniformity of the holographic gratings and increases the recording speed. Theoretical simulations agree with experimental results.     

磺化聚苯乙烯/聚乙烯醇交联膜的制备与性能

以磺化度为75%的磺化聚苯乙烯(SPS)和聚乙烯醇(PVA)为原料,按一定的配比共混后浇铸成膜,在程序升温的过程中进行热交联,通过控制不同交联时间得到不同交联密度的交联膜.考察了交联膜的离子交换容量(IEC)、吸水率、溶胀性和尺寸稳定性;利用原子力显微镜和交流阻抗仪对交联膜的表面形貌及电导率进行了表征.结果表明:交联膜的IEC值略有降低;吸水率和溶胀度得到了很好的控制,具有较好的尺寸稳定性;膜表面出现了明显的亲水相和憎水相相分离,且亲水相微区的聚集尺寸和连续性随交联时间的长短而变化;随交联时间的延长,交联膜的电导率值略有下降,但交联后膜的室温电导率仍高于0.01 S/cm.     

Synthesis of a mesoporous silica hollow microsphere using polyvinyl alcohol

A mesoporous silica hollow microsphere was synthesized in the presence of polyvinyl alcohol for the first time. The synthesized material was characterized by various instrumental techniques such as small-angle X-ray scattering, scanning electron microscopy, transmission electron microscopy, N₂ adsorption measurement and Fourier transform infrared spectroscopy. I have succeeded in incorporating an Ultraviolet ray absorber, 2, 2´, 4, 4´ tetrahydroxy benzophenone by mixing it after synthesis. However an attempt to incorporate by mixing before synthesizing it changes the morphology. In addition to polyvinyl alcohol, the use of other polymers such as polyvinyl pyrrolidine and polyethylene glycol also changes the morphology into dry leaves or fibers.