12 research outputs found

    Preparation of biomimetic photo-responsive polymer springs

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    This protocol describes the preparation of polymer springs that twist under irradiation with light, in a manner that mimics how plant tendrils twist and turn under the effect of differential expansion in different sections of the plant. The artificial springs are typically 1 mm in width, 50 ╬╝m in thickness and up to 10 mm in length, their length being limited by cell dimensions only. They are made from polymer networks that keep memory of a liquid crystalline order, and in which an azobenzene derivative is introduced covalently as a molecular photo-switch. This liquid crystal polymer is prepared by irradiation of a twist cell filled with a mixture of shape-persistent liquid crystals, liquid crystal having reactive end groups, molecular photo-switches, some chiral dopant and a small amount of photo-initiator. This cell is assembled out of two glass slides separated by a spacer and covered by a thin film of polyimide that was rubbed along the long axis of the cell for the bottom slide, and along the short axis of the cell for the top slide. Once the cell is filled by capillarity, photo-polymerization takes place at 48 ┬║C and takes approximately 1.5 h. The product is a photo-responsive liquid crystal polymer network that is characterised by optical microscopy, scanning electron microscopy and tensile strength measurements. The film is post-cured overnight at 60┬║C. Removing the resulting soft polymer film and cutting out the desired spring-like shape takes ~45 min. The springs operate at ambient temperature, by mimicking the orthogonal contraction mechanism that is at the origin of plant coiling. They are shape shifting under irradiation with ultraviolet light and can be pre-programmed to either wind or unwind, as encoded in their geometry. Once illumination is stopped, the springs return to their initial shape in ambient light conditions

    Conversion of light into macroscopic helical motion.

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    A key goal of nanotechnology is the development of artificial machines capable of converting molecular movement into macroscopic work. Although conversion of light into shape changes has been reported and compared to artificial muscles, real applications require work against an external load. Here, we describe the design, synthesis and operation of spring-like materials capable of converting light energy into mechanical work at the macroscopic scale. These versatile materials consist of molecular switches embedded in liquid-crystalline polymer springs. In these springs, molecular movement is converted and amplified into controlled and reversible twisting motions. The springs display complex motion, which includes winding, unwinding and helix inversion, as dictated by their initial shape. Importantly, they can produce work by moving a macroscopic object and mimicking mechanical movements, such as those used by plant tendrils to help the plant access sunlight. These functional materials have potential applications in micromechanical systems, soft robotics and artificial muscles

    Przewodnictwo usieciowanych ┼╝ywic epoksydowych zawieraj─ůcych grup─Ö bifenylow─ů

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    Conductivity of two epoxy matrices based on the same monomer was compared. The epoxy monomer had symmetric structure and contained the biphenyl group which induced additional phase transitions in the pure material. Two amines responsible for different curing mechanisms were used to prepare the matrices. Wide ohmic regions were observed in both materials but quite high activation energy results in quick drop of conductivity at low temperatures and the materials can be treated as good isolators below 100┬░C. The obtained results are comparable with traditional epoxy resins.Por├│wnano przewodnictwo dw├│ch matryc epoksydowych, opartych na tym samym monomerze. Monomer epoksydowy mia┼é budow─Ö symetryczn─ů i zawiera┼é grup─Ö bifenylow─ů, kt├│ra wp┼éyn─Ö┼éa na powstanie dodatkowych przej┼Ť─ç fazowych w czystym materiale. Do wytworzenia matryc u┼╝yto dw├│ch amin odpowiedzialnych za r├│┼╝ne mechanizmy sieciowania. W obu materia┼éach zaobserwowano szerokie przedzia┼éy przewodnictwa omowego, ale du┼╝a energia aktywacji powoduje szybki spadek przewodnictwa w niskich temperaturach i poni┼╝ej 100┬░C materia┼éy te mog─ů by─ç traktowane jak dobre izolatory. Otrzymane wyniki s─ů por├│wnywalne z tradycyjnymi ┼╝ywicami epoksydowymi