Monodisperse poly(styrene-b-semifluorinated side chain) block copolymers were synthesized by anionic polymerization of poly(styrene-b-1,2/3,4-isoprene) followed by the corresponding polymer analogous reactions. By controlling the block copolymer composition and the relative lengths of the fluorocarbon and hydrocarbon units in the side group, the effect of chemical structure on surface properties and the influence of liquid crystalline structure of the semifluorinated side chain on the surface behavior were evaluated. The composition of side groups does not greatly affect the as-prepared sample surface tension, but influences instead the transition temperatures of the room temperature liquid crystal phase. It was observed that the shorter fluorocarbon units (six −CF2− units) form a smectic A phase at room temperature. The critical surface tension of the SA phase is 10.8 mN/m, and the polymer surface undergoes significant reconstruction when immersed in water. However, when the fluorocarbon side chain contains more than eight −CF2− units, the resulting surface possesses a lower critical surface tension (ca. 8 mN/m) and exhibits negligible surface reconstruction. We believe the stability results from the highly ordered packing of the room temperature smectic B phase. This mesophase resists the reconstruction of the surface, since to do so would require loss of the enthalpies of transition. The estimated activation energy to destroy the smectic B phase is about 3−10 times higher than that of smectic A phase. This phase forms a uniform, hexagonally packed −CF3 terminated surface with a low critical surface tension similar to that of fluorocarbon-based Langmuir−Blodgett films. The self-assembly of these liquid crystalline block copolymers at both the molecular and microstructural level provides a valuable approach to creating stable, low surface energy materials.

Rod-coil block copolymers are self-assembling polymers that combine the physics of orientational ordering of rodlike polymers and the microphase separation of coil-coil block copolymers. Several new solid-state morphologies were observed in a series of anionically synthesized model poly(hexyl isocyanate-b-styrene) rod-coil diblock copolymers examined by transmission electron microscopy and selected-area electron diffraction. The rod-coils formed smectic C-like and O-like morphologies with domain sizes ranging from tens of nanometers to almost 1 micrometer. Both structural and orientational changes were found for increasing rod volume fractions. In addition, some morphologies exhibited spontaneous long-range orientational order over many tens of micrometers.

No abstract

The synthesis and characterization of a family of well-defined liquid crystal−coil (LC−coil) diblock copolymers have been carried out. The block copolymers in this study have been designed to have nearly identical molecular weight azobenzene-containing LC blocks in order to eliminate possible variations in LC behavior caused by the differences in the LC block molecular weight. Quantitative hydroboration chemistry was used to convert the pendent double bonds of an isoprene block to hydroxyl groups to which the mesogenic groups were attached via acid chloride coupling. The LC homopolymer and the block copolymers (LC volume fraction from f LC = 0.82 to f LC = 0.20) all exhibited smectic mesophases with similar clearing transition temperatures. The clearing transition enthalpies strongly depend on the block composition ratio and decrease as the LC block volume fraction decreases. Solvent-casting of a lamellar LC−coil copolymer (SICN5-66/60) resulted in an oriented bulk film in which both the axes of the mesogenic groups and the lamellar interfaces lie parallel to the film surfaces. A LC cylinder morphology was observed with a f LC = 0.22 LC-containing block (SICN5-176/55) using TEM and confirmed by SAXS measurements. This is the first observation with the LC block in a cylinder microdomain. Other morphologies (bicontinuous, LC sphere) were observed by TEM while retaining the smectic order in the LC microphase.

Biodegradable and biocompatible elastic materials for soft robotics, tissue engineering or stretchable electronics with good mechanical properties, tunability, modifiability, or healing properties drive technological advance, yet they are not durable under ambient conditions nor combine all attributes in a single platform. We have developed a versatile gelatin-based biogel, which is highly resilient with outstanding elastic characteristics yet degrades fully when disposed. It self-adheres, is rapidly healable and derived entirely from natural and food-safe constituents. We merge for the first time all favorable attributes in one material that is easy to reproduce, scalable and low-cost in production under ambient conditions. This biogel is a step towards durable, lifelike soft robotic and electronic systems that are sustainable and closely mimic their natural antetypes. Main: In 2025, an estimated 6 million tons of garbage will be generated per day 1 , with tech disposables being a rapidly growing contributor. End-of-lifetime appliances contain valuable materials that are laborious in recovery or toxic substances that are readily released into nature through landfilling or improper treatment 2. Biodegradable 3-6 and transient systems 7 are promising routes towards closing the loop on waste generation and create new opportunities for secure systems, but often at the cost of compromises in performance. Complex biological systems bridge this gap. They unite seemingly antagonistic properties-tough yet adaptive, durable and self-healing yet degradable-allowing them to perform a myriad of intricate tasks. Embodiments of technologies that intimately interface with humans naturally benefit from mimicking such soft, functional forms. A range of biomimetic systems 8 including soft machines 9 and electronic skins 10 achieve a high level of functionality by introducing self-healing 11,12 , intrinsic stretchability 13 , or the insightful merging of soft-to-hard materials 14. Waste flow issues and in vivo applications that avoid multiple surgeries are tackled with inextensible devices in the form of edible 3,15 and transient electronics 7,16. However, introducing stretchability to degradable devices remains challenging. Recent approaches focusing on stretchable biodegradable sensors 5 require expensive materials and are still wired to bulky measurement systems hindering implementation as wearable devices. Challenges here stem from the diverse material requirements,