Chromogenic Photonic Crystal Sensors Enabled by Multistimuli‐Responsive Shape Memory Polymers

Here novel chromogenic photonic crystal sensors based on smart shape memory polymers (SMPs) comprising polyester/polyether‐based urethane acrylates blended with tripropylene glycol diacrylate are reported, which exhibit nontraditional all‐room‐temperature shape memory (SM) effects. Stepwise recovery of the collapsed macropores with 350 nm diameter created by a “cold” programming process leads to easily perceived color changes that can be correlated with the concentrations of swelling analytes in complex, multicomponent nonswelling mixtures. High sensitivity (as low as 10 ppm) and unprecedented measurement range (from 10 ppm to 30 vol%) for analyzing ethanol in octane and gasoline have been demonstrated by leveraging colorimetric sensing in both liquid and gas phases. Proof‐of‐concept tests for specifically detecting ethanol in consumer medical and healthcare products have also been demonstrated. These sensors are inexpensive, reusable, durable, and readily deployable with mobile platforms for quantitative analysis. Additionally, theoretical modeling of solvent diffusion in macroporous SMPs provides fundamental insights into the mechanisms of nanoscopic SM recovery, which is a topic that has received little examination. These novel sensors are of great technological importance in a wide spectrum of applications ranging from environmental monitoring and workplace hazard identification to threat detection and process/product control in chemical, petroleum, and pharmaceutical industries.     

Molding Micropatterns of Elasticity on PEG‐Based Hydrogels to Control Cell Adhesion and Migration

We present an innovative and simple, soft UV lithographic method “FIll‐Molding In Capillaries” (FIMIC) that combines soft lithography with capillary force driven filling of micro‐channels to create smooth hydrogel substrates with a 2D micro‐pattern on the surface. The lithographic procedure involves the molding of a polymer; in our case a bulk PEG‐based hydrogel, via UV‐curing from a microfabricated silicon master. The grooves of the created regular line pattern are consequently filled with a second hydrogel by capillary action. As a result, a smooth surface is obtained with a well‐defined pattern design of the two different polymers on its surface. The FIMIC method is very versatile; the only prerequisite is that the second material is liquid before curing in order to enable the filling process. In this specific case we present the proof of principle of this method by applying two hydrogels which differ in their crosslinking density and therefore in their elasticity. Preliminary cell culture studies on the fabricated elasticity patterned hydrogels indicate the preferred adhesion of the cells to the stiffer regions of the substrates, which implies that the novel substrates are a very useful platform for systematic cell migration studies, e.g. more fundamental investigation of the concept of “durotaxis”.     

Plasmapolymerschichten als Basis für maßgeschneiderte funktionale Oberflächen

Plasmapolymer coatings for tailor‐made functional surfaces The tailoring of surface properties via polymer coatings is currently a strongly pursued topic in various fields ranging from microsystem technology to bioanalytics. A precise tuning of surface properties, however, is only possible if chemically well‐defined processes are used that usually require reactive surface moieties to which molecules can be coupled. In this contribution we summarize studies that aimed at the modification of inert surfaces. For this purpose reactive groups at the surfaces are generated by plasma polymerisation of allyl amine which results in layers that contain amino groups. Initiator molecules for free radical polymerization processes are then coupled to these amino groups resulting in surfaces from which polymers can then be grown via surface‐initiated polymerization. Using these processes, polymer monolayers with very different properties can be generated by simply using different monomers.     

A finite strain framework for the simulation of polymer curing. Part II. Viscoelasticity and shrinkage

A phenomenologically inspired, elastic finite strain framework to simulate the curing of polymers has been developed and discussed in the first part (Hossain et al. in Comput Mech 44(5):621–630, 2009) of this work. The present contribution provides an extension of the previous simulation concept towards the consideration of viscoelastic effects and the phenomenon of curing shrinkage. The proposed approach is particularly independent of the type of the free energy density, i.e. any phenomenologically or micromechanically based viscoelastic polymer model can be utilised. For both cases the same representatives that have been used for the elastic curing models, i.e. the Neo-Hookean model and the 21-chain microsphere model, are reviewed and extended accordingly. The governing equations are derived as well as the corresponding tangent operators necessary for the numerical implementation within the finite element method. Furthermore, we investigate two different approaches—a shrinkage strain function and a multiplicative decomposition of the deformation gradient–to capture the phenomenon of curing shrinkage, i.e. the volume reduction induced by the polymerisation reaction which may lead to significant residual stresses and strains in the fully cured material. Some representative numerical examples conclude this work and prove the capability of our approach to correctly capture inelastic behaviour and shrinkage effects in polymers undergoing curing processes.     

Plasmachemische Gasphasenabscheidung – eine Technologie zur Deposition organischer und anorganischer Schichten. Plasma Enhanced Chemical Vapor Deposition – a Thin Film Technique for Organic and Inorganic Layers

Plasma enhanced chemical vapor deposition (PECVD) has a wide range of interest for thin films up to some μm thickness. It has widespread applications for high quality dielectric and semiconducting silicon alloys at deposition temperatures below 450 °C and pressures at 1 mbar on plane substrates and attracts growing attention for the surface modification of polymers. The PECVD takes advantages of the possibility to alter the film properties in a wide range easily, and the coatings can achieve a variety of useful properties unobtainable by other coating techniques. An environmentally friendly plasma chemical reactor etch cleaning of SiO_x, SiN_x and other film materials can be applied by changing the process gas and without breaking the vacuum. PECVD can be used in a fixed substrate and continuous substrate flow mode. An capacitively coupled parallel‐plate electrode assembly using radio‐frequency (RF) excitation of the discharge is most widely used for substrate areas up to a few square meters. Among the capacitively excitation an inductively and electromagnetically excitation at frequencies in the RF and UHF range has also succeeded in achieving a high rate PECVD. Two applications are presented to show the characteristics and the potential of this technique, the PECVD of semiconducting hydrogenated amorphous silicon, intrinsic or doped, with low power densities using monosilane as a source gas for solar cells, thin films transistors and digital image sensors and the plasma polymerisation of organosilicon protection layers employing the HMDSO monomer and high power densities for mirrors and lenses.     

Aqueous compatible polymers in bionanotechnology

Core-shell molecularly imprinted particles (CS-MIPs) have been synthesised using the technique of emulsion polymerisation with caffeine and theophylline being used in the surface template polymerisation with ethylene glycol dimethacrylate and oleylphenyl hydrogen phosphate. A radiolabelling study with caffeine-8-14C showed that the template was completely located at the particle surface during polymerisation. Caffeine could be specifically bound to a caffeine-imprinted CS-MIP to give a biphasic Scatchard binding curve, whereas the binding profile to a theophylline-imprinted CS-MIP was monophasic. The nanoparticles have the potential to be used in the molecular recognition of small molecules in a complex biological matrix. Water soluble highly-branched imidazole end-chain functionalised polymers of nanodimensions have also been synthesised via reversible addition-fragmentation chain transfer polymerisation. The polymers have lower critical solution temperatures which occur at sub-ambient temperatures and have proven useful in the affinity precipitation of proteins which are particularly temperature sensitive, e.g. the histidine-tagged protein fragment BRCA1. An overview of both of these areas of research is described outlining the diversity of these aqueous compatible polymers in molecular recognition processes at the nanoscale.     

A small-strain model to simulate the curing of thermosets

This contribution presents a newly developed phenomenological model to describe the curing process of thermosets undergoing small strain deformations. The governing equations are derived from a number of physical and chemical presuppositions and details of the numerical implementation within the finite element method are given. The curing of thermosets is a very complex process involving a series of chemical reactions which result in the conversion of liquid low molecular weight monomer mixtures into highly cross-linked solid macromolecular structures. This phase transition from a viscous fluid to a viscoelastic solid can be modelled by a constitutive relation which is based on a temporal evolution of shear modulus and relaxation time. Some numerical examples demonstrate the capability of the model to correctly represent the evolution of elastic and inelastic material properties as well as the volume shrinkage taking place during the curing process.     

Nanokristalline Werkstoffe hergestellt mit dem Thermischen HF‐Plasma

Nano‐crystalline materials manufactured with the Thermal RF‐Plasma The Inductively Coupled Plasma (ICP) at atmospheric pressure is particularly suited for melting and evaporation of materials. The electrodeless ICP can be generated without limitation of the kind of plasma forming gases. Therefore, using an argon‐oxygen gas mixture as sheath gas of the ICP nanophase coatings can be processed by synthesis with metal‐organic liquid precursors injected in the hot plasma core. For depositions, the plasma jet has to be supersonic. For particles which impinge onto the substrate placed near the nozzle exit of the plasma torch thin and dense coatings are obtained with crystallite sizes of 30‐ 40 nm. The composition and the grain size of as‐deposited coatings are analyzed by XRD.     

Quantitative control of RTM6 epoxy resin polymerisation by optical index determination

RTM6 epoxy resin curing is usually characterized by the polymerisation degree. We report in this paper on a refractive index measurement technique applied on an experimental mould to control, quantitatively and in situ, the industrial RTM process. For the first time, we determined simultaneously the thermo-optical coefficient, the refractive index evolution, the specific volume and the polymerisation degree of the resin. The calculation of a “polymerisation degree optical coefficient” led to a quantification of the RTM6 epoxy resin polymerisation process. This calibration coefficient is very useful to perform a real time industrial process control. Furthermore, the optoelectronic system is connected to a data processing unit and is easy to use in an industrial environment.     

电子束作用下树脂体系的固化行为

根据电子束固化复合材料树脂体系的原理,从引入辐敏性的基团入手,合成了含硅丙烯酸酯的活性稀释剂、芳香族酰亚胺活性单体、含丙烯酸的PMR型聚酰胺酸和单官能、双官能的马来酰亚胺单体。在此基础上,对合成所得到的产物和几种环氧树脂进行了辐射交联实验,并考察与分析了不同树脂的辐射固化反应行为。与此同时对合成所得产物进行了表征,对固化物性能进行初步测试。所得研究结果,对电子束固化树脂体系的进一步研究具有重要的参考价值。      

Funktionelle Schichten durch UV‐ und Elektronenstrahlhärtung

UV (EB) Curable Functional Coatings Composition, curing kinetics and application potential of acrylate based UV(EB) curable coatings are described. To formulate these coatings a manifold of acrylate oligomers exhibiting either ether, ester, epoxy or urethane functionality can be used as binders whereas acrylate monomers are applied as reactive thinners. Coatings with special functional properties such as resistance against chemicals, scratch and abrasion resistance, UV‐protection and flexibility can be applied on substrates such as paper, plastic films, wood and engineered wood, aluminum etc. Additionally, liquid acrylates can be favourably applied to produce microstructured or super smooth surfaces: the acrylate is brought into contact with either a structurized or a polished drum and rapidly cured in contact with the cylinder surface. Scratch and abrasion resistant coatings are obtained from acrylate nanocomposites. These formulations contain up to 30 w% SiO₂ nanoparticles covered by a polysiloxane shell.     

Freeform,Reconfigurable Embedded Printing of All‐Aqueous 3D Architectures

Aqueous microstructures are challenging to create, handle, and preserve since their surfaces tend to shrink into spherical shapes with minimum surface areas. The creation of freeform aqueous architectures will significantly advance the bioprinting of complex tissue‐like constructs, such as arteries, urinary catheters, and tracheae. The generation of complex, freeform, three‐dimensional (3D) all‐liquid architectures using formulated aqueous two‐phase systems (ATPSs) is demonstrated. These all‐liquid microconstructs are formed by printing aqueous bioinks in an immiscible aqueous environment, which functions as a biocompatible support and pregel solution. By exploiting the hydrogen bonding interaction between polymers in ATPS, the printed aqueous‐in‐aqueous reconfigurable 3D architectures can be stabilized for weeks by the noncovalent membrane at the interface. Different cells can be separately combined with compartmentalized bioinks and matrices to obtain tailor‐designed microconstructs with perfusable vascular networks. The freeform, reconfigurable embedded printing of all‐liquid architectures by ATPSs offers unique opportunities and powerful tools since limitless formulations can be designed from among a breadth of natural and synthetic hydrophilic polymers to mimic tissues. This printing approach may be useful to engineer biomimetic, dynamic tissue‐like constructs for potential applications in drug screening, in vitro tissue models, and regenerative medicine.     

Abiotic oxidation of catechol by soil metal oxides

The mechanism of catechol oxidation by soil metal oxides is investigated in a slurry reactor. This abiotic transformation is shown to consist in a three-step process. The first step is a heterogeneous reaction. Catechol undergoes fast, partial oxidation at the expenses of Fe and Mn oxides contained in the soil. In the second step, reduced Fe and Mn are released into the aqueous solution and immediately complexed by catechol. Metal-catecholate complexes are stable at the very low dissolved-oxygen concentration levels attained under nitrogen sparging. The third step is a homogenous reaction. The highly reactive intermediate produced by catechol partial oxidation initiates catechol polymerisation. Under nitrogen sparging, the polymerisation process ends rather rapidly, thus yielding only partial conversion of the phenol and producing low-molecular weight, water-soluble polymers. Further oxidation of the metal-catecholate complexes formed in the second step only occurs under air sparging. Thus, reactive intermediates are formed at much higher concentration levels than those attained when nearly no oxygen is present in solution. The polymerisation proceeds at a much faster rate until, under the experimental conditions adopted, complete catechol conversion is attained and high-molecular-weight, insoluble polymers are produced.     

Kunststoffoptiken mit Antireflex‐ und Antibeschlageigenschaften durch Plasmaätzen und Beschichtung

Plastic optics exhibiting anti‐reflection and anti‐fogging properties produced by plasma etching and coating Plasma treatments are capable to generate antireflective surface structures on various polymers. On PMMA a self organized surface with nep‐like bumps exhibits excellent optical properties. Many other materials like polycarbonate, zeonex and lacquers can be etched after depositing a very thin initial layer to form a more holey structure. These surfaces attain high transmission values too and can be better stabilized by coatings than the nep‐ structure on PMMA. Interesting for practical applications are hydrophilic top‐layers to provide anti‐fogging properties in combination with improved transmission.     

A finite strain framework for the simulation of polymer curing. Part I: elasticity

A phenomenologically motivated small strain model to simulate the curing of thermosets has been developed and discussed in a recently published paper (Hossain et al. in Comput Mech 43(6):769–779, 2009). Inspired by the concepts used there, this follow-up contribution presents an extension towards the finite strain regime. The thermodynamically consistent framework proposed here for the simulation of curing polymers particularly is independent of the choice of the free energy density, i.e. any phenomenological or micromechanical approach can be utilised. Both the governing equations for the curing simulation framework and the necessary details for the numerical implementation within the finite element method are derived. The curing of polymers is a very complex process involving a series of chemical reactions typically resulting in a conversion of low molecular weight monomer solutions into more or less cross-linked solid macromolecular structures. A material undergoing such a transition can be modelled by using an appropriate constitutive relation that is distinguished by prescribed temporal evolutions of its governing material parameters, which have to be determined experimentally. Part I of this work will deal with the elastic framework whereas the following Part II will focus on viscoelastic behaviour and shrinkage effects. Some numerical examples demonstrate the capability of our approach to correctly reproduce the behaviour of curing materials.     

Großflächige Quellen f�r die industrielle Plasmatechnik

Plasma‐technological processes in modern thin film technologies for the refinement of surfaces are of constantly growing interest. Plasma‐technical procedures for the surface modification and film deposition mainly are contributed to the low pressure regime and use ion and/or plasma techniques. In particular plasma‐technological process concepts in the industrial field require adapted and scalable large area plasma sources. A new source concept, based on a coaxial structure, unites these specifications and permits plasma arrangements of nearly any required size.     

3D Printing by Multiphase Silicone/Water Capillary Inks

3D printing of polymers is accomplished easily with thermoplastics as the extruded hot melt solidifies rapidly during the printing process. Printing with liquid polymer precursors is more challenging due to their longer curing times. One curable liquid polymer of specific interest is polydimethylsiloxane (PDMS). This study demonstrates a new efficient technique for 3D printing with PDMS by using a capillary suspension ink containing PDMS in the form of both precured microbeads and uncured liquid precursor, dispersed in water as continuous medium. The PDMS microbeads are held together in thixotropic granular paste by capillary attraction induced by the liquid precursor. These capillary suspensions possess high storage moduli and yield stresses that are needed for direct ink writing. They could be 3D printed and cured both in air and under water. The resulting PDMS structures are remarkably elastic, flexible, and extensible. As the ink is made of porous, biocompatible silicone that can be printed directly inside aqueous medium, it can be used in 3D printed biomedical products, or in applications such as direct printing of bioscaffolds on live tissue. This study demonstrates a number of examples using the high softness, elasticity, and resilience of these 3D printed structures.     

Polymers Move in Response to Light

Significant advances have recently been made in the development of functional polymers that are able to undergo light‐induced shape changes. The main challenge in the development of such polymer systems is the conversion of photoinduced effects at the molecular level to macroscopic movement of working pieces. This article highlights some selected polymer architectures and their tailored functionalization processes. Examples include the contraction and bending of azobenzene‐containing liquid‐crystal elastomers and volume changes in gels. We focus especially on light‐induced shape‐memory polymers. These materials can be deformed and temporarily fixed in a new shape. They only recover their original, permanent shape when irradiated with light of appropriate wavelengths. Using light as a trigger for the shape‐memory effect will extend the applications of shape‐memory polymers, especially in the field of medical devices where triggers other than heat are highly desirable.     

Wirtschaftliche Anwendung von Mikrowellen‐Plasmen vom mittleren bis Atmosphärendruck. Economic utilisation of microwave excited plasma in medium to atmospheric pressure

An overview on the potential of medium to atmospheric pressure processes will be given and discussed in context to production applications. The introduction of the medium to atmospheric pressure plasma source is a huge progress and a valuable, attractive tool. The plasma source bases on the concept of cy lindrical r esonator with annu lar s lots (CYRANNUS®). High process speed and reliability are the most important facts for technical applications. Parameters as gas/flow dynamic can be controlled and lead to further improvements of equipment and process design. The CYRANNUS® plasma is used in down‐stream configuration for several applications such as glass films on polymer substrate to reduce oxygen permeation, protective coatings against corrosion or wear and hydrophilic or hydrophobic surface properties. Also etching or cleaning can be done easily because of arbitrary process gas in the plasma source. The advantage of medium pressure is higher supply of reactive species and improved transportation of reaction products. Various processes with plasma surface interaction are discussed from physical and technical viewpoint as plasma enhanced CVD, plasma polymerisation on metal or polymer substrates. Using the advantages of medium pressure plasma processes consequently leads to new design of equipment and material flow. In‐line/on‐line treatment of 3‐D material becomes most efficient and enables competitive plasma processes for mass productions. For diamond deposition a larger size of the plasma at high pressure processes are essential for a device with best economics.     

Dielectric analysis of light-curing dental restorative materials—a pilot study

This study tested the potentiality of dielectric analysis (DEA) for determining the reaction performance of light-curing dental resins. The influence of polymerisation conditions and material properties on the ion viscosity were investigated within a current field. The restoratives were light-cured for 20, 40 or 60 s in a layer thickness between 1, 2 , or 3 mm with a varying distance between curing light and specimen of 1, 3 or 5 mm. The tests were performed at 25°C/37°C with different polymerisation modes. Nine restoratives (two composites and their derivate flowables, two ormocers, one compomer, one nano-filled composite and one siloran) were investigated. The ion-viscosity-time graph was analysed to characterize reaction velocity and polymerisation conversion. The slope of the ion viscosity decreased with increasing distance between polymerisation light and specimen. The time of exposure affected the affinity and the conversion, with a polymerisation maximum at 40 s. A relation between thickness and reaction time and between polymerisation modus and conversion/velocity was found. The temperature influenced the reaction affinity. Different materials showed an individual curing performance. DEA-monitoring of the ion viscosity gives principal insight in the polymerisation reaction of light curing materials. Further investigations are necessary for identifying the relation between ion viscosity and polymerisation.