Light‐Driven Side‐On Nematic Elastomer Actuators

Abstract

photonics and electronics, ranging from the relatively simple nanoscale emitter and complementary logic that can be obtained from single nanorod p±n junctions. Moreover, the direct growth of modulation-doped nanorods eliminates the lithographic steps used to create doped nanotube p±n junctions. [18,19] Therefore, we believe that controlled growth of modulation-doped nanorod p±n junctions represents an advance over previous work. [9,11,18±20] Experimental GaN nanorods were grown in a horizontal HVPE system. In the growth process, the Ga precursor (7N) was synthesized in the lower region of the reactor, via the reaction of HCl gas (5N) (in an N 2 diluent gas) with Ga metal (at 750 C), to form GaCl. This precursor was then transported to the substrate area, where it was mixed with NH 3 (6N4) to form GaN at 478 C (substrate temperature). After the furnace was cooled to room temperature, a dark yellow layer was found on the surface of the substrate.Nanorods dispersed in methanol were deposited onto oxidized silicon substrates, and electrical contacts were fabricated using focused ion beam (FEI company, Strata DB 235) lithography. GaN nanorod LED contacts were fabricated by a two-step process in which the n-type contact (first step) was made using Ti/Al (100 nm/200 nm) by electron-beam evaporation and then was annealed at 950 C for 30 s to form an ohmic contact. In the second step, the p-type contact was made using Ni/Au (100 nm/200 nm) by electron-beam evaporation and then was annealed at 600 C for 30 s to form an ohmic contact. Electrical transport measurements were made using a home-made system under computer control. In order to investigate the optical properties of GaN nanorod p±n junctions, we carried out cathodoluminescence (CL) spectroscopy and imaging. The CL spectra of the nanorod at room temperature were taken in a high-resolution scanning electron microscope (SEM, FEI company, XL 30 SFEG) combined with a CL system (Gatan, MONOCL2) having a 1200 lines/mm grating blazed at 500 nm. The emission was detected using a Peltier-cooled photomultiplier. The maximum spectral resolution is 0.2 nm. The experimental conditions in CL spectroscopy were carefully established to minimize the undesired influence of electron-beam bombardment on the conditions of the specimens.

Bursting of sensitive polymersomes induced by curling

“…The mesogenic unit in the side-on LC block contains an azobenzene group, which undergoes a trans-to-cis configurational transition upon UV exposure. This isomerization induces a nematic (N) to isotropic (I) transition in the LC polymer (24) causing a conformational change of the chain from a rod to a coil (20,21). Fig.…”

“…To implement this approach, we prepared asymmetric polymersomes in which each leaflet consisted of a different type of diblock copolymer: One copolymer was insensitive to any remote stimulus whereas the hydrophobic moiety of the second copolymer was a liquid-crystalline (LC) polymer. LC phases are known to respond to magnetic/electric fields, temperature (18), or light (if the mesogen is a chromophore) (19), and LC polymers have been shown to change conformation in response to some of these stimuli (20)(21)(22). As an inert copolymer, we selected polyethyleneglycol-b-polybutadiene (PEG-b-PBD, or PBD for simplicity) (1).…”

Reduced time as a unified parameter determining fixity and free recovery of shape memory polymers

“…In general, the polymer's shape memory (SM) effect is described and evaluated in a thermo-temporal SM cycle, where the SMP is firstly deformed at a high temperature (usually above the glass transition or melting point) and subsequently frozen upon cooling to fix the programmed temporary shape. When an environmental stimulus is applied, the SMP could either provide recovery stresses or return to their permanent shapes, depending on whether or not the external loads still exist, namely the constrained or free recovery condition [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] . Since SMPs can sense the environmental changes and then take reactions in a predetermined sequence with deformation, they are considered as a promising alternative for the future's spontaneous shape changing and tunable components in various applications such as microelectromechanical systems, surface patterning, biomedical devices, aerospace deployable structures and morphing structures [31][32][33][34][35][36][37][38][39] .…”

Monitoring the Contractile Properties of Optically Patterned Liquid Crystal Based Elastomers

“…We can notice a difference between the curvature of the two curves. Figure 22 represents the behavior of the order parameter obtained by polarized Fourier transform spectroscopy (FTIR) in the case of the same elastomer [45]. If we compare the simulation curve with figure 22 we can see that they have the same apparence.…”