The goal of this study is to use
ABA triblock copolymers with central
bottlebrush B segments and crystalline linear chain A segments to
demonstrate the effect of side chains on the formation and mechanical
properties of physical networks cross-linked by crystallites. For
this purpose, a series of bottlebrush copolymers was synthesized consisting
of central amorphous bottlebrush polymer segments with a varying degree
of polymerization (DP) of poly(n-butyl acrylate)
(PnBA) side chains and linear tail blocks of crystallizable
poly(octadecyl acrylate-stat-docosyl acrylate) (poly(ODA-stat-DA)). The materials were generated by sequential atom
transfer radical polymerization (ATRP) steps starting with a series
of bifunctional macroinitiators followed by the growth of two ODA-stat-DA linear-chain tails and eventually growing poly(nBA) side chains with increasing DPs. Crystallization of
the poly(ODA-stat-DA) tails resulted in a series
of reversible physical networks with bottlebrush strands bridging
crystalline cross-links. They displayed very low moduli of elasticity
of the order of 103–104 Pa. These distinct
properties are due to the bottlebrush architecture, wherein densely
grafted side chains play a dual role by facilitating disentanglement
of the network strands and confining crystallization of the linear-chain
tails. This combination leads to physical cross-linking of supersoft
networks without percolation of the crystalline phase. The cross-link
density was effectively controlled by the DP of the side chains with
respect to the DP of the linear tails (n
A). Shorter side chains allowed for crystallization of the linear
tails of neighboring bottlebrushes, while steric repulsion between
longer side chains hindered the phase separation and crystallization
process and prevented network formation.
A ring type frequency selective surface (FSS) can provide transmission stop-band characteristics in rooms. This allows adjacent rooms to be isolated for one LAN for frequency reuse while other frequencies pass through the walls with minimal attenuation. The FSS was screen printed on a thin flexible plastic substrate of permittivity 3.2 with a stop band at 12.3GHz and 10dB bandwidth of 3.5GHz. The variation in bandstop characteristics was investigated for various wall materials. The centre frequency varied by more than 3 GHz for common wall materials which means significant transparency for some building materials. The technique is a low cost method of confining LAN picocells in one room.
A substrate-integrated waveguide (SIW) cavitybacked antenna with two slots on top of the cavity has been proposed in this paper. The bowtie slot is the main radiator of the cavity and a rectangular slot close to the feed point has been etched (to add extra resonance to enhance the bandwidth of the antenna in the desired frequency range). Tuning the rectangular slot improved the fractional bandwidth to 8%. A 7.9 dBi peak gain and a steady beam over the entire bandwidth are achieved. The FTBR (front to back ratio) of the antenna is more than 20 dBi. A standard PCB producing process has been used in order to manufacture the proposed antenna on a single layer substrate.
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