Gerrit ten Brinke

Self-assembly of polymeric supramolecules is a powerful tool for producing functional materials that combine several properties and may respond to external conditions. We illustrate the concept using a comb-shaped architecture. Examples include the hexagonal self-organization of conjugated conducting polymers and the polarized luminance in solid-state films of rodlike polymers obtained by removing the hydrogen-bonded side chains from the aligned thermotropic smectic phase. Hierarchically structured materials obtained by applying different self-organization and recognition principles and directed assembly form a basis for tunable nanoporous materials, smart membranes, preparation of nano-objects, and anisotropic properties, such as proton conductivity.

ABSTRACT: Depending on the spinning and drawing conditions, two crystal structures for solution-spun poly(L-lactide) are obtained. The pseudoorthorhombic a structure (a = 10.6, b = 6.1, and c = 28.8 A) contains two chains in the unit cell and is found at relatively low drawing temperatures and/or low hot-draw ratios. At higher drawing temperatures and/or higher hot-draw ratios a second so-called 0 structure appears. For this structure an orthorhombic unit cell is proposed (a = 10.31, b = 18.21, and c = 9.00 A) containing six chains. The chain conformations of the a and p structure are left-handed 10/3 and 3/1 helices, respectively. Calculations show that both conformations have approximately the same energy. Therefore, the preference for one of the two structures is determined by packing considerations. In fibers containing a mixture of CY and 0 structure, the latter seems to bear most of the load during stress-strain experiments. Meridional small-angle X-ray scattering experiments yield a maximum for fibers containing only a structure pointing to a lamellar folded-chain morphology. The (3 structure on the other hand seems to correspond to a fibrillar morphology. Differential scanning calorimetry on unconstrained fibers shows that the 0 structure melts at a lower temperature than the a structure. The large shift of the peak melting temperature to higher temperatures in melting experiments on constrained fibers indicates that both lamellae and fibrils contribute to the strength of the fibers. This points to a considerable amount of interconnections/ entanglements between adjacent lamellae. 1.

It was demonstrated that polymeric supramolecular nanostructures with several length scales allow straightforward tailoring of hierarchical order-disorder and order-order transitions and the concurrent switching of functional properties. Poly(4-vinyl pyridine) (P4VP) was stoichiometrically protonated with methane sulfonic acid (MSA) to form P4VP(MSA)1.0, which was then hydrogen-bonded to pentadecylphenol. Microphase separation, re-entrant closed-loop macrophase separation, and high-temperature macrophase separation were observed. When MSA and pentadecylphenol were complexed to the P4VP block of a microphase-separated diblock copolymer poly[styrene-block-(4-vinyl pyridine)], self-organized structures-in-structures were obtained whose hierarchical phase transitions can be controlled systematically. This microstructural control on two different length scales (in the present case, at 48 and 350 angstroms) was then used to introduce temperature-dependent transitions in electrical conductivity.

A recently introduced mean field theory of phase behavior in polymer/ copolymer systems is extended to random copolymer/ copolymer systems. Miscibility in these systems does not require any specific interaction but rather a "repulsion" between the different covalently bonded monomers of the copolymers. Conversely, immiscibility may occur in systems with specific interaction due to an "attraction" between the different covalently bonded monomers of the copolymers. Using the mean field approach, we discuss in detail the phase behavior in polymer/ copolymer systems. The requirements for the occurrence of a symmetric or an asymmetric (im)miscibility window in a temperature-copolymer composition diagram are derived. Using this treatment, we calculate all the segmental interaction parameters for blends of poly(2,6-dimethyl-1,4-phenylene oxide) with poly(o-chlorostyrene-co-p-chlorostyrene), poly(o-fluorostyrene-co-p-fluorostyrene), poly(styrene-co-o-chlorostyrene), poly(styrene-co-p-chlorostyrene), poly(styrene-co-o-fluorostyrene), and poly(styrene-co-p-fluorostyrene). The absence of miscibility in blends of poly(2,6-dimethyl-1,4-phenylene oxide) with any poly(o-bromostyrene-co-p-bromostyrene) copolymer is explained.

Combination of self-assembly at different length scales leads to structural hierarchies. It offers rich possibilities to construct nanostructured matter, nanoscale parts, and switching (responsive) properties based on the phase transitions of the self-assembled structures. Complexation of oligomeric amphiphiles to polymers using ionic interactions, coordination, or hydrogen bonding leads to polymeric comb-shaped supramolecules (complexes), which self-assemble at a length scale of a few nm. Self-assembly at an order of magnitude larger length scale is provided by block copolymers, and combination of the latter two concepts leads to structural hierarchies. They provide e.g. templates for mesoporous materials and nano-objects, and allow switching conductivity and switching optical properties. Structural hierarchies are also observed by complexing moderately monodisperse polymeric rods with amphiphiles. Finally, self-assembly at even a larger length scale upon using colloidal particles may be combined to the above structures, as encouraged by recent observations.