PREPARATION OF HIGH-TEMPERATURE VULCANIZED SILICONE RUBBER OF EXCELLENT MECHANICAL AND OPTICAL PROPERTIES USING HYDROPHOBIC NANO SILICA SOL AS REINFORCEMENT

Hydrophobic nano silica sol(HNSS)was incorporated into polyvinylmethylsiloxane to prepare reinforced high- temperature vulcanized(HTV)silicone rubber.HTV silicone rubber filled with 40 phr HNSS showed excellent mechanical and optical properties:the tensile strength reached 11.7 MPa and the optical transmittance was higher than 90%.Possible reasons for reinforcement and transparency were discussed on the basis of the bound rubber percentage,total crosslink density,and SEM analysis.Our work suggests that H...     

Structure-Property Relationships in Rubber-Modified Styrenic Polymers

Styrenic polymers and copolymers are often impact modified with rubber particles. The efficiency of rubber toughening depends mainly on the size of the rubber particles and the degree of cross-linking. The deformation rate, the temperature, the orientation of the polymer molecules and the efficiency of rubber grafting also influence rubber toughening. It is thought that on impact, cavitation inside the rubber particles occurs which reduces the detrimental dilatational stress in the bulk polymer without forming cracks in the brittle matrix or at the rubber-matrix interface. Crazing and shearing are facilitated if the rubber particles can easily cavitate. This can be achieved by either avoiding too much cross-linking or by adding oil (silicone oil in the case of ABS) into the rubber particles, which acts as nuclei for void formation. An electron spectroscopic imaging method is described which allows visualizing the location of the oil. Already after cooling silicone oil modified ABS samples down to liquid nitrogen temperature rubber cavitation is observed. This cavitation is caused by the thermal stress developing due to the differences in thermal expansion coefficient between the rubber phase and the SAN-matrix and is facilitated by silicone oil. Voiding also leads to an increase of light scattering, which can be detected by an optical microscope using dark field illumination.     

A study of the mixing of a liquid into an elastomer

A low-melting alloy was mixed with SBR and carboxy-NBR on a rubber mill above its melting point, and changes in its state of dispersion were examined through an optical microscope. Solution of the resulting mix showed that many of the particles of alloy were of colloid size, and did not settle out. Repeated washing of the sediment with solvent could not separate all the rubber phase from the sediment, and a form of bound rubber is postulated.     

Design and Synthesis of Transparent Poly （acrylonitrile-butadiene-styrene） and Relationship Between Its Phase Construction and Transparency

IntroductionABS resins have been widely applied to the field ofengineering materials because of their excellent me-chanical,electrical,physical,and chemical proper-ties.Typically,ABS resins comprise a rigid copolymermatrix-phase dispersed in a graft copol…     

Polydomains in liquid-crystal elastomers

In liquid-crystal elastomers, the simultaneous presence of rubber elasticity due to the crosslinked backbone chains and of optical birefringence due to the mesogens in the side chains lead to exceptional physical properties. An elastic deformation of the network influences the order of the mesogens and, therefore, the optical properties. A theory based on a Landau-de Gennes expansion of the free energy is proposed. In the opaque polydomain phase, the local orientation is given by a compromise between the external mechanical field and a local anchoring interaction. As the field is increased, it becomes energetically favorable for the mesogens to align parallel to the mechanical field, and a transition to a transparent monodomain structure occurs. Results for the average orientation, the stress and the chain conformation are given.     

顺丁橡胶的聚集态结构及其拉伸行为

用电子显微镜及光学显微镜研究了高顺式1,4-聚丁二烯橡胶的聚集态结构及其对力学性能的影响。观察了样品的低温结晶、室温下的溶胶和凝胶结构,及其拉伸和松弛过程。证明在室温下,无定形结构的顺丁橡胶内部并不是均匀的,而是具有一定规整度的区域所组成。其基本单元为链结(nodule),链球(Aggre-gation of nodules),及胶团(cluster of gel)。结构单元及其连接均与分子量及凝胶含量有关。这些结构因素均通过超分子结构而影响拉伸及松弛行为。     

Orientational birefringence of uniaxially compressed PMMA networks in the unswollen state

Swollen PMMA networks show significant deviations from the theory of rubber elasticity. The unusual mechanical, optical and swelling properties have been explained by the existence of associations, well known for PMMA solutions.Unswollen PMMA networks show stress optical properties which are very similar to the networks swollen in carbon tetrachloride which is known as a strong complexing solvent. This indicates that associations exist in the bulk material. Swelling in carbon tetrachloride does not change the content of associations, only the glass transition temperature is reduced.Increasing the amount of crosslinking agent proves that the stress optical coefficient depends on the crosslinking density. This is contrary to the theoretical predictions. An explanation given by the effect of short network chains is not satisfactory. However, the consideration of a crosslinking chain instead of a crosslinking point gives a sufficient explanation. An oriented crosslinking chain gives a positive contribution to the total optical anisotropy while a PMMA chain shows a change from negative values (hindered rotation) to positive values (free rotation).Part I in Colloid & Polym Sci 262:182 (1984)Deceased Sept. 4, 1984     

双烯类液体橡胶的研发进展

液体橡胶作为合成橡胶的重要种类,是室温下能流动的橡胶材料。本文介绍了液体橡胶的性能特点及分类,着重阐述了双烯类液体橡胶即液体聚丁二烯橡胶、液体丁腈橡胶、液体异戊橡胶、液体丁苯橡胶和液体氯丁橡胶的结构特征、性能特点及主要用途,并进一步探讨了它们的研发、生产和使用情况。液体橡胶便于实现生产连续化和自动化,且加工方便,顺应时代发展的"低碳"潮流。从产品种类、牌号,应用范围等方面对今后的发展提出了建议。     

Micromechanisms of failure in short-fiber-reinforced high-impact polystyrene under tensile loading

Injection-molded, short-glass-fiber-reinforced high-impact polystyrene was investigated under uniaxial tension with special attention to the effects of fiber and rubber concentration on fracture behavior. According to a fracture morphology study performed by polarized optical and scanning electron microscopy, crazes were consecutively initiated from rubber-styrene composite particles and from fiber ends. The rubber particles exhibited an intra-particle failure mode which resulted from the failure manner of the matrix becoming of a more brittle character with increasing fiber fraction. Fibers were surrounded by neigh boring growing crazes. Failure at the fiber-matrix interfaces proceeded with an increase in the number of crazes. With increasing concentration of the fibers, crazing at rubber particles appeared to be suppressed and crazing occurred more preferentially at the fiber ends, which accelerated a macroscopic fracture.Dedicated to Prof. H. H. Kausch on the occasion of his 60th birthday.     

Fibre-optic fluorescing sensor for ammonia

The fluorescing sensor is based on the change in fluorescence intensity of a buffered pH indicator solution entrapped in silicone rubber. Exposure to ammonia increases the pH of the trapped solution; this increases the fluorescence intensity, which is monitored via an optical fibre bundle. Ammonium chloride in 0.001 M sodium hydroxide, or the indicators themselves, can serve as buffers. Effects of sensor preparation and buffer composition on response time, reversibility and sensitivity are discussed.     

Thermo-oxidative aging in surface layer of cis-1,4-polybutadiene vulcanizates

A study of the microstructural changes occurring in the surface layer of cis-1,4-polybutadiene (BR) vulcanizates during thermo-oxidative aging in the temperature range of 120–180°C was carried out by using optical microscope, SEM, MIR–IR, XPS, and swelling. The physical properties, structural changes, and interreaction between rubber and filler (clay) in the surface layer comparing with the center bulk of BR vulcanizates are observed.     

Nematic and smectic liquid single crystal elastomers: Influence of external stress parallel and perpendicular to the director

The influence of uniaxial mechanical stress applied parallel or perpendicular to the director axis (optical axis) of nematic and smectic-A elastomers having a permanent macroscopically ordered monodomain structure is investigated. Due to the different phase structures applying an external mechanical stress leads to completely different responses with respect to the young moduli and reorientation processes of the director. Nematic elastomers exhibit a weak anisotropy of the moduli parallel (μ₁₁ and perpendicular (μ) to the optical axis with μ₁₁ / μ = 1.5. The moduli are mainly determined by the rubber elasticity of the poly(siloxane) network. Applying the mechanical stress perpendicular to the initial director axis causes a rotation of the director axis that is connected with a periodic pattern formation and a ‘soft elastic’ response. For smectic-A elastomers μ₁₁/μ is in the order of 10². While μ reflects a rubber elastic response similar to that of the nematic system, μ₁₁ indicates an enthalpy-elastic behaviour of the one-dimensional long range order of the smectic layers. In this direction reorientation of the phase structure with a deformation of the smectic layers occurs above a threshold elongation. In contrast to the nematic networks, a deformation perpendicular to the optical axis causes no director reorientation, displaying the liquid-like properties within the smectic layers.     

Anisotropic thermal transport in a crosslinked polyisoprene rubber subjected to uniaxial elongation

Anisotropic thermal transport in a crosslinked polyisoprene (natural rubber) subjected to uniaxial elongation is investigated experimentally. Using a novel optical technique based on forced Rayleigh scattering, two components of the thermal diffusivity tensor are measured as a function of stretch ratio. The thermal diffusivity is found to increase in the direction parallel, and decrease in the direction perpendicular, to the stretch direction. The level of anisotropy for the natural rubber is substantially lower than that reported by Tautz 50 years ago but comparable to that found in our previous studies on molten polymers, quenched thermoplastics, and other crosslinked elastomers. Thermal diffusivity data along with measurements of the tensile stress were used to evaluate the stress‐thermal rule, which was found to be valid over the entire range of stretch ratios. In contrast, failure of the stress‐optic rule was observed at stretch ratios well below the largest value at which the stress‐thermal rule was valid. This suggests that the degree of anisotropy in thermal conductivity depends on both orientation and stretch of polymer chain segments. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Synthesis and thermal polymerization of perylene bisimide containing benzocyclobutene groups

Fourfold benzocyclobutene-functionalized perylene bisimide（PBI 4） has been synthesized and its structure was characterized by FTIR,MS and NMR.PBI 4 can react either with itself,or the appropriate dienophiles to form the corresponding products under appropriate temperature.The polymer film obtained from the reaction of PBI 4 with methyl vinyl silicone rubber possessed excellent film forming properties including flatness.The optical properties of PBI 4 and polymer film obtained from the reaction of PBI 4 and methyl vinyl silicone rubber have been determined by UV/vis and fluorescence spectroscopy.     

胶粉在改性沥青中的物化行为分析

生产胶粉改性沥青(CRMA)是实现废橡胶资源化利用及减轻环境污染的有效途径。为了研究胶粉在沥青中的物理及化学行为,采用邻苯二甲酸二丁酯(DBP)模拟沥青的轻组分,将胶粉置入DBP中,在175℃下,反应1.5 h后分离胶粉与轻组分,对轻组分进行气相色谱与质谱联用(GC-MS)分析,讨论胶粉与轻组分发生的物理化学作用;对不同条件下制备的胶粉改性沥青分离胶粉后进行红外光谱(IR)和差示扫描量热(DSC)分析,研究橡胶改性沥青中的官能团变化和热力学特性。结果表明,分离胶粉后的DBP中存在19种检出物,除含量最高的DBP外,其余物质均为胶粉浸出物或与轻组分的反应产物,即胶粉在轻组分中发生了复杂的物理化学反应。胶粉沥青样品中的—CH_2和C=C双键等特征官能团吸收峰大幅增强,橡胶分子在沥青中发生断链降解释放出小分子物质溶于沥青组分发挥改性作用;195℃、1.5 h和175℃、3.0 h制备的沥青样品DSC谱线出现了强烈的吸热峰,即处理温度过高或时间过长,可能发生胶粉过度降解、胶粉团聚或沥青老化行为,使胶粉改性沥青的物化状态发生改变,导致性能劣化。从胶粉物化变化的角度,建议制备胶粉改性沥青时,胶粉掺量(质量分数)应在20%左右,处理温度不高于195℃,处理时间不超过1.5 h。     

Characterization of Optical Fiber Dissolved Oxygen Sensor for Aquaculture Sensing and Monitoring

Optical fiber sensor using sol gel membrane incorporated RTV silicon rubber was fabricated and developed for the characterization of dissolved oxygen in aqueous solution. The sol gel materials used consists of Tetraethylorthosilicate (TEOS) and Triethoxyoctylsilane (Octyl-triEOS) as the precursor compound for the preparation of the sol gel structures, while tris-BP Ruthenium (II) chloride as the fluorescent lifetime of the oxygen indicator. Dip coating techniques is utilized to position the sol gel technology at the distal end of the optical fiber. Dissolved oxygen gas sensor characterizations include a study on the sensitivity, temperature effects and drift rate of the sensor performance when measured in 40ppt salt water. Potential applications of the optical fiber sensor are including aquaculture, river monitoring and environment sector.     

Liquid single crystal elastomers (lsce) - mechanical optical and electric properties

Liquid crystal elastomers can be macroscopically ordered with respect to the director by applying a mechanical field similar to electric/magnetic field effects of low molar mass liquid crystals. Introducing network anisotropy a priori by the synthesis, uniformly aligned nematic or smectic elastomers are available without external mechanical field. These LSCE's combine optical properties of single crystals with entropy elasticity of elastomers. Due to uniform director orientation without defects, the LSCE's exhibit excellent transparency which makes them applicable for optical elements. Non-linear optical properties can be easily optimized by attaching suitable I.c.-moieties to the polymer network. On the other hand, due to the rubber elasticity of the LSCE's, electromechanical effects can be observed, e. g. piezoelectricity of chiral smectic C-LSCE's.     

Optical tweezers applied to a microfluidic system

We will demonstrate how optical tweezers can be combined with a microfluidic system to create a versatile microlaboratory. Cells are moved between reservoirs filled with different media by means of optical tweezers. We show that the cells, on a timescale of a few seconds, can be moved from one reservoir to another without the media being dragged along with them. The system is demonstrated with an experiment where we expose E. coli bacteria to different fluorescent markers. We will also discuss how the system can be used as an advanced cell sorter. It can favorably be used to sort out a small fraction of cells from a large population, in particular when advanced microscopic techniques are required to distinguish various cells. Patterns of channels and reservoirs were generated in a computer and transferred to a mask using either a sophisticated electron beam technique or a standard laser printer. Lithographic methods were applied to create microchannels in rubber silicon (PDMS). Media were transported in the channels using electroosmotic flow. The optical system consisted of a combined confocal and epi-fluorescence microscope, dual optical tweezers and a laser scalpel.     

Relation between stress and segmental orientation during mechanical cycling of a natural rubber‐based compound

X‐ray diffraction technique is used to evaluate the evolution of the segmental orientation in a natural rubber sample during mechanical uniaxial stretching and in the Gaussian regime condition. The method proves to be sensitive enough for testing the validity of the stress‐optical law. Measurements are performed at different temperatures and show that the dependence of the orientation parameter upon elongation is very close to the prediction of classical phantom theories. On the contrary, a significant Mooney–Rivlin correction is needed to account for the stress–strain relation. Consequently, systematic deviations from the stress‐optical law are observed, in particular for elongations below 2. These deviations are adverse from predictions of both the constrained and the diffuse junction theories. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 943–950