Influence of variations in liquid-crystalline content upon the self-assembly behavior of siloxane-based block copolymers

Verploegen, Eric; Zhang, Tejia; Murlo, Nicholas; Hammond, Paula T.

doi:10.1039/b800212f

Cited by 26 publications

(37 citation statements)

References 35 publications

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“…The low q scattering arises from the larger smectic layers, which are more readily disrupted, thus leading to a shift in the peak upon continued exposure; the larger smectic layers are less tightly packed and thus the photoisomerization has a lower enthalpic barrier that must be overcome. A similar phenomenon was previously observed in related systems, in which larger smectic layers had a lower smectic‐to‐isotopic transition temperature 17…”

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Reversible Switching of the Shear Modulus of Photoresponsive Liquid‐Crystalline Polymers

et al. 2009

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Liquid crystalline polymers (LCP) have attracted recent interest due to their ability to combine the properties of small molecule liquid crystals and those of a polymer [1] . Liquid crystalline moieties can be designed to exhibit a conformational change on the molecular level in response to thermal [2,3] , pH [3] , electrical [4] or optical [5, 6] stimulation. Liquid crystalline polymeric materials benefit from the rheological integrity that the polymer component provides to the system. Siloxane based LCPs present specific advantages associated with the very low glass transition temperature (T g ) of the siloxane backbone [7,8] , allowing for the materials to retain their properties over a wide temperature range, particularly at room temperature.The utilization of photoisomerization of LC moieties to produce actuator materials was first proposed by deGennes [5] . This class of materials can be stimulated by exposure to particular wavelengths of electromagnetic radiation (e.g. visible light), resulting in molecular rearrangements that manifest the desired effects. The molecular conformational change can lead to a change in the rheological or dimensional properties of the materials, resulting in photoresponsive shape memory polymers [9] or films that exhibit a bending actuation when one surface is exposed to light [8, 10] . There are several examples of molecules that have Correspondence to: Paula Hammond, hammond@mit.edu. garnered great interest for their abilities to photoisomerize and thus generate useful properties in polymers [11, 12] . One such class of molecules is azobenzene-containing moieties, which have been found to undergo a trans to cis photoisomerization upon exposure to UV (366 nm) light. The moiety relaxes to the equilibrium trans conformation when the UV irradiation is removed; this relaxation can also be accelerated with heat or exposure to longer wavelength light (> 540 nm). The photoisomerization of azo moieties incorporated into a polymer matrix have been shown to disrupt the stability of nematic [13] and smectic [14] LC mesophases. Thus, a reversible and isothermal smectic to isotropic transition can be achieved by disrupting the smectic LC mesophase through the isomerization of the azo moieties [11,15] . NIH Public AccessHere we will demonstrate the effects of UV stimulation upon the morphology and rheological properties of azo-containing siloxane-based LCPs. To date, a very limited number of studies have addressed the light-tunable rheological properties of photoresponsive polymeric systems. Among them, the recent work by Ketner et al. [16] revealed the remarkable potential of aqueous micellar solutions whose viscosity can drop by more than four orders of magnitude upon UV exposure. The limiting factor in their study is the irreversible character of the transformation. In the present work, we demonstrate reversible rheological property changes. Such properties are of particular interest for light activated damping mechanisms, actuable armor, and related applications in fields such as...

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“…The polymer backbone used in this study is a poly(vinylmethylsiloxane) (PVMS) with a number average molecular weight ( M n ) of 14 800 g mol −1 and a polydispersity index (PDI) of 1.23 17. The homopolymer can be modified with a broad range of attachment percentages by using previously reported approaches that rely on platinum‐catalyzed hydrosilyation.…”

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Reversible Switching of the Shear Modulus of Photoresponsive Liquid‐Crystalline Polymers

et al. 2009

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“…Scheme 1 shows the chemical structure of the side chain liquid crystalline block copolymer used, where the ratio y / (y + z) is the LC attachment percent. A detailed characterization of the structure, morphology, thermal, and mechanical properties of these side-chain liquid crystalline block copolymers has been previously reported29. Spin casting was used to produce films between 100 nm and 250 nm in thickness; the self-assembly behavior was not variant with the film thickness over this range.…”

Section: Effect Of Liquid Crystal Content Upon the Orientation Of Cylmentioning

confidence: 99%

“…4BPP4 denotes the structure of the LC moiety29. The smectic to isotropic transition temperature (T iso ) was determined via differential scanning calorimetry (DSC).…”

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Controlling the Morphology of Side Chain Liquid Crystalline Block Copolymer Thin Films through Variations in Liquid Crystalline Content

et al. 2008

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In this paper we describe methods for manipulating the morphology of side-chain liquid crystalline block copolymers through variations in the liquid crystalline content. By systematically controlling the covalent attachment of side chain liquid crystals to a block copolymer (BCP) backbone, the morphology of both the liquid crystalline (LC) mesophase and the phase segregated BCP microstructures can be precisely manipulated. Increases in LC functionalization lead to stronger preferences for the anchoring of the LC mesophase relative to the substrate and the inter-material dividing surface (IMDS). By manipulating the strength of these interactions the arrangement and ordering of the ultrathin film block copolymer nanostructures can be controlled, yielding a range of morphologies that includes perpendicular and parallel cylinders, as well as both perpendicular and parallel lamellae. Additionally, we demonstrate the utilization of selective etching to create a nanoporous liquid crystalline polymer thin film. The unique control over the orientation and order of the self-assembled morphologies with respect to the substrate will allow for the custom design of thin films for specific nano-patterning applications without manipulation of the surface chemistry or the application of external fields. Keywords liquid crystal; block copolymer; thin films; selective etchingRecently there has been a great deal of research directed at controlling the self-assembly of block copolymer thin films, with specific interest in obtaining the desired orientation of nanoscale features relative to the substrate, such as perpendicular or parallel cylinders 1, 2 . Progress has been made in controlling the morphologies of block copolymer thin films through techniques such as solvent annealing 3, 4 , zone casting 5 , electric field alignment 6 , optical alignment 7 , topographical patterning 8, 9 , and chemical substrate patterning 10-12 . Due to the large interfacial area of thin films, the orientation of the domains depends greatly upon the relative surface energies of the blocks 13-16 . We will show that the incorporation of a liquid crystalline (LC) component into such systems offers a powerful tool for manipulating the Hammond@mit.edu. orientation of the self-assembled structures. When an LC component is introduced, several factors such as conformational asymmetry, structural asymmetry, and the anchoring of the LC mesophase to the inter-material dividing surface (IMDS) can alter the self-assembly behavior 17-24 . The two possible scenarios for smectic LC anchoring relative to an interface -such as a substrate or the IMDS -are homeotropic or homogeneous, where the smectic layer normal is perpendicular or parallel to the interface, respectively. It has been shown that the LC mesophase will preferentially orient with respect to the IMDS due to surface stabilization effects 25-27 . In this way a well oriented block copolymer mesophase can be used to template order in the LC mesophase. Additionally, liquid crystalline polymers (LCP) are ...

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“…Observed morphologies of poly- mer liquid crystal (6), from AFM, shows the formation of regular patterns where the distances between interdigitated multilayer polymer chains are 15 nm. (Figure 6) [37,38]. The thermotropic behavior of (4) and (6) in bulk was studied by two-dimensional X-ray wide-angle scattering (2D-WAXS).…”

Section: Phase Behavior Studiesmentioning

confidence: 99%

Synthesis and thermotropic behavior of side chain polysiloxane bearing triphenylene moiety

Makowski¹,

Ganicz²,

Zaja̧czkowski³

et al. 2015

Express Polym. Lett.

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Abstract. Side chain discotic polysiloxane with 2,3,6,7-tetrakis(hexyloxy)-10-methoxytriphenylene-11-undecanoate moieties is synthesized by hydrosilylation reaction. The phase behavior and thermooptical properties of the polysiloxane and the side chain precursor 2,3,6,7-tetrakis(hexyloxy)-10-methoxytriphenylene-11-undecanoate are examined by polarizing optical microscopy, thermooptical analysis, differential scanning calorimetry and wide angle X-ray scattering studies. A columnar planar alignment of LC in the layers has been determined. The pronounced alignment makes this polymer a promising material for application in optoelectronic devices. The differences in phase transitions and morphology between the triphenylene precursor and the discotic polysiloxane are discussed.

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Influence of variations in liquid-crystalline content upon the self-assembly behavior of siloxane-based block copolymers

Cited by 26 publications

References 35 publications

Reversible Switching of the Shear Modulus of Photoresponsive Liquid‐Crystalline Polymers

Reversible Switching of the Shear Modulus of Photoresponsive Liquid‐Crystalline Polymers

Controlling the Morphology of Side Chain Liquid Crystalline Block Copolymer Thin Films through Variations in Liquid Crystalline Content

Synthesis and thermotropic behavior of side chain polysiloxane bearing triphenylene moiety

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