A smectic main-chain liquid crystalline elastomer (LCE), with controlled shape memory behavior, is synthesized by polymerizing a biphenyl-based epoxy monomer with an aliphatic carboxylic acid curing agent. Microstructures of the LCEs, including their liquid crystallinity and crosslinking density, are modified by adjusting the stoichiometric ratio of the reactants to tailor the thermomechanical properties and shape memory behavior of the material. Thermal and liquid crystalline properties of the LCEs, characterized using differential scanning calorimetry and dynamic mechanical analysis, and structural analysis, performed using small-angle and wide-angle X-ray scattering, show that liquid crystallinity, cross-linking density, and network rigidity are strongly affected by the stoichiometry of the curing reaction. With appropriate structural modifications it is possible to tune the thermal, dynamic mechanical, and thermomechanical properties as well as the shape memory and thermal degradation behavior of LCEs. ■ INTRODUCTIONShape memory polymers (SMP) are a category of smart materials that are able to return to their original shape from a deformed state when exposed to external stimuli. SMPs generally consist of cross-linked polymer networks, which determine the permanent shape of the material, and switching segments, which can be oriented and solidified to fix a temporary shape. 1 The shape recovery is driven by the entropic force of the switching domains which tend to gain entropy and return to a random conformation when undergoing phase transitions, such as glass transition, liquid crystalline (LC) transition, and melting transition. 2,3 Liquid crystalline elastomers (LCE) represent a special class of SMPs that are defined by a reversible LC phase transition and a unique coupling between LC mesogens and polymer networks. They exhibit reversible shape change when exposed to external stimuli, such as heat, 4 light, 5−8 or magnetic field, 9,10 which makes them excellent candidates for artificial muscles, sensors, lithography substrates, and shape memory materials. 11−16 A number of LCEs with different LC phases and network structures have been synthesized and characterized, including nematic main-chain, 17−19 smectic main-chain, 20,21 nematic sidechain, 22,23 and smectic side-chain LCEs. 24−26 These materials exhibit a wide variety of shape memory and actuating behaviors. However, in spite of their promising properties and remarkable potential, practical applications of LCEs are limited because of the difficulties encountered when tailoring thermal transition temperatures and thermomechanical properties of the materials for end-use applications. Several methods have been proposed to prepare LCEs with tunable shape memory properties. A smectic main-chain LCE has been designed and synthesized through copolymerization of two benzoate-based vinyl monomers with different LC phase transition temperatures. 27 It has been shown that both LC transition and thermomechanical properties of LCEs could be tailored by changing the ...

The structure of the extremely proton-rich nucleus 11 8 O3, the mirror of the two-neutron halo nucleus 11 3 Li8, has been studied experimentally for the first time. Following two-neutron knockout reactions with a 13 O beam, the 11 O decay products were detected after two-proton emission and used to construct an invariant-mass spectrum. A broad peak of width ∼3 MeV was observed. Within the Gamow coupled-channel approach, it was concluded that this peak is a multiplet with contributions from the four-lowest 11 O resonant states: J π =3/2 − 1 , 3/2 − 2 , 5/2 + 1 , and 5/2 + 2. The widths and configurations of these states show strong, non-monotonic dependencies on the depth of the p-9 C potential. This unusual behavior is due to the presence of a broad threshold resonant state in 10 N, which is an analog of the virtual state in 10 Li in the presence of the Coulomb potential. After optimizing the model to the data, only a moderate isospin asymmetry between ground states of 11 O and 11 Li was found.

Particle-decaying states of the light nuclei 11,12 N and 12 O were studied using the invariant-mass method. The decay energies and intrinsic widths of a number of states were measured, and the momentum correlations of three-body decaying states were considered. A second 2p-decaying 2 + state of 12 O was observed for the first time, and a higher energy 12 O state was observed in the 4p+2α decay channel. This 4p+2α channel also contains contributions from fission-like decay paths, including 6 Beg.s.+ 6 Beg.s.. Analogs to these states in 12 O were found in 12 N in the 2p+ 10 B and 2p+α+ 6 Li channels. The momentum correlations for the prompt 2p decay of 12 Og.s. were found to be nearly identical to those of 16 Neg.s., and the correlations for the new 2 + state were found to be consistent with sequential decay through excited states in 11 N. The momentum correlations for the 2 + 1 state in 12 O provide a new value for the 11 N ground-state energy. The states in 12 N/ 12 O that belong to the A=12 isobaric sextet do not deviate from the quadratic isobaric multiplet mass equation (IMME) form.

We report the design of a mass spectrometer featuring an ion source that delivers ions directly into high vacuum from liquid inside a capillary with a sub-micrometer-diameter tip. The surface tension of water and formamide is sufficient to maintain a stable interface with high vacuum at the tip, and the gas load from the interface is negligible, even during electrospray. These conditions lifted the usual requirement of a differentially pumped system. The absence of a background gas also opened up the possibility of designing ion optics to collect and focus ions in order to achieve high overall transmission and detection efficiencies. We describe the operation and performance of the instrument and present mass spectra from solutions of salt ions and DNA bases in formamide and salt ions in water. The spectra show singly charged solute ions clustered with a small number of solvent molecules.