Giant surfactants are size-amplified counterparts of small-molecule surfactants with one (or more) molecular nanoparticle(s) (MNPs) as head(s). The tail components include but are not limited to polymer chains. The combination of the MNP heads having diverse symmetries and surface functionalities with the tails possessing variable compositions and architectures generates an enormously large family of giant surfactants. The recent progresses on their solution self-assembly behaviors are briefly summarized in this chapter. In general, this class of materials could self-organize into a great variety of ordered supramolecular structures in solution. While the self-assembly shares many general principles of small molecule surfactants and block copolymers, these giant surfactants possess their own unique phase behaviors and structural characteristics, which has been found to be sensitive to their primary chemical structures and molecular topologies. The exploration of the universal principles that govern their self-assemblies will provide guidance to the rational design and manipulation of new functional materials for technologically relevant applications.
The behavior of giant amphiphilic molecules at the air-water interface has become a subject of concern to researchers. Small changes in the molecular structure can cause obvious differences in the molecular arrangement and interfacial properties of the monolayer. In this study, we have systematically investigated the interfacial behaviors of the giant amphiphilic molecules with different number of hydrophobic BPOSS blocks and one hydrophilic ACPOSS block ((BPOSS)n-ACPOSS (n = 1-5)) at the air-water interface by the surface pressure-area (π-A) isotherm, Brewster angle microscopy (BAM), compression modulus measurement, and hysteresis measurement. We found that both the number of BPOSS blocks and the compression rate can significantly influence the interfacial behaviors of giant molecules. The π-A isotherms of giant molecules (BPOSS)n-ACPOSS (n = 2-5) exhibit a "cusp" phenomenon which can be attributed to the transition from monolayer to multilayer. However, the cusp is dramatically different from the "collapse" of the monolayer studied in other molecular systems, which is highly dependent on the compression rate of the monolayer. In addition, the compression modulus and hysteresis measurements reveal that the number of BPOSS blocks of (BPOSS)n-ACPOSS plays an important role in the static elasticity, stability, and reversibility of the Langmuir films.
Form-stable phase change fibers (PCFs), that are composed of stable supporting material (as polymer matrix) and phase change material (PCM, as working ingredient) have become novel smart materials and are widely applied in energy storage, thermal regulation and biomedical field. However, the inherent limitation of PCF is the restriction of the supporting material on the crystallization of the PCM, which results in low phase change enthalpy (ΔH). Here, six different types of PCF comprised of poly(lactic acid) (PLA, as supporting material) and poly(ethylene glycol) (PEG, as PCM) have been fabricated and their morphology, phase change performance and structural transition during phase change have been extensively studied. We reveal that the crystallizability and glass transition temperature of PLA have a dominating influence on ΔH. In the optimum system, PLA/PEG PCFs can achieve up to 104 J/g ΔH which is close to the theoretical value of pristine PEG. This high-performance PCF also exhibits only 2.5% ΔH loss after 100 thermal cycles and good ability in thermal energy storage and thermal regulation. This work provides a promising form-stable PCF and introduces a new strategy towards developing high ΔH PCFs by selecting suitable supporting materials.
Self-assembly is a process in which a disordered system spontaneously develops ordered structures without external directions. In materials science and technology, self-assembly in the bulk has been extensively utilized to fabricate desired microscopic structures. Rodlike molecules have emerged as one of the most promising molecular building blocks to construct functional materials. Although the self-assembly of conventional molecules containing rodlike components generally results in nematic or layered smectic phases, extensive efforts have revealed that rational molecular design provides a versatile platform to engineer rich self-assembled structures. In their Review article on page 6741 ff., Feng, Lin and Cheng et al. summarize the first successes achieved in polyphilic liquid crystals and rod–coil block systems. Special attention is paid to recent progress in the conjugation of rodlike building blocks with other molecular building blocks through the molecular Lego approach.
The inherent statistical heterogeneities associated with chain length, composition, and architecture of synthetic block copolymers compromise the quantitative interpretation of their self-assembly process. This study scrutinizes the contribution of molecular architecture on phase behaviors using discrete ABA triblock copolymers with precise chemical structure and uniform chain length. A group of discrete triblock copolymers with varying composition and symmetry were modularly synthesized through a combination of iterative growth methods and efficient coupling reactions. The symmetric ABA triblock copolymers self-assemble into long-range ordered structures with expanded domain spacings and enhanced phase stability, compared with the diblock counterparts snipped at the middle point. By tuning the relative chain length of two end blocks, the molecular asymmetry reduces the packing frustration, and thus increases the order-to-disorder transition temperature and enlarges the domain sizes. This study would serve as a quantitative model system to correlate the experimental observations with the theoretical assessments and to provide quantitative understandings for the relationship between molecular architecture and self-assembly.
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