The self-assembling adsorption/quaternization of a (dialky1amino)stilbazole nonlinear optical chromophore precursor onto benzyl chlorideprefunctionalized surfaces is studied in situ by polarized second harmonic generation techniques. The measurements reveal that the self-assembly kinetics are approximately biexponential ( I x 2 -(1 --a l k z t ) ) with a rapid initial phase, followed by a slower second phase. The in situ measurements also indicate that the average tilt angle of the chromophore dipole moment direction with respect to the surface normal increases significantly ( -20" -42O) in the initial phases of chromophore adsorption and then remains nearly constant. These results suggest substantial chromophor-hromophore electrostatic and steric repulsion as monolayer growth proceeds. The maximum chromophore coverage observed corresponds to -49 A2/ molecule and x(2) = 3 X lO-' esu at X = 1064 nm.

The progress and extent of nucleophilic substitution and ion exchange reactions of self-assembled chromophoric monolayers are studied by X-ray photoelectron (XPS) and second harmonic generation (SHG) spectroscopy. Self-assembled monolayers prepared from 2-[4-(chloromethyl)phenyl]ethyl trichlorosilane (1) on glass substrates are susceptible to nucleophilic substitution of ∼90% of the surface-confined benzylic chloride functionalities with the “hypernucleophile” 4-(dimethylamino)pyridine; however, only ∼60% of the densely packed benzyl chloride groups undergo reaction with the high-β chromophore precursor 4‘-[4-[N,N-bis(3-hydroxypropyl)amino]styryl]pyridine (2a). Quaternization of a benzylic monolayer with this molecule yields a monolayer having a bulk second-order NLO response (χ(2)) of 3 × 10-7 esu at λ0 = 1064 nm, corresponding to a near-maximum chromophore coverage of ∼2 × 1014 molecules/cm2. The kinetics of this substitution reaction and associated structural modifications are studied in real time by in situ polarized SHG techniques, which reveal non-Langmuirian kinetics and a rapidly increasing chromophore tilt angle with increasing coverage. The quaternization kinetics can be fit to a phenomenological biexponential rate equation with k‘1 ≈ 2 × 10-2 L mol-1 s-1 and k‘2 ≈ 2 × 10-3 L mol-1 s-1 and to a coverage-dependent activation energy model (E A = E 0 + E bθ), yielding a perturbative energy E b of 6−8 kJ mol-1. Both models are compatible with increasing repulsive interactions between chromophores at high coverages. The charge-compensating chloride counterions within monolayers having dense chromophore packing can be ion exchanged with iodide, up to a maximum of ∼40% of available chloride ions. The introduction of larger anions (sulfanilate, ethyl orange, eosin B) is observed in less densely packed films; however, the ion exchange process is completely inhibited in monolayers capped with a siloxane overlayer. In all cases, exchange of the chloride leads to significant increases in the second-harmonic generation efficiency, up to 45% on exchange with eosin B. In the case of iodide and sulfanilate substitution for chloride, the increase in the second-order response upon ion exchange is attributable to the incoming anion assuming a position within the monolayer microstructure different from that of the displaced anion.

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In some special circumstances (e.g., tsunamis, battlefields, and earthquakes), communication infrastructures are damaged or nonexistent. For communication among people, mobile smart devices (MSDs) can be used to construct mobile ad hoc networks (MANETs). This paper focuses on the problem of data delivery in MANETs aiming to improve the quality of service (QoS) and quality of experience (QoE) users receive. MANETs, however, have the well-known problems of frequent disconnections and high rates of failed transmissions as MSDs move in and out of network coverage areas, and the topology constantly changes. To solve these issues, the main contributions of this work are as follows: (1) we provide and investigate the QoE-driven multipath TCP (MPTCP)-based data delivery model in MANETs; (2) we present hidden Markov model-based optimal-start multipath routing, which can effectively predict a mobile node's near future network connection state according to its past connection state; (3) we leverage MPTCP to simultaneously transmit data via multiple interfaces of MSDs and improve the establishment method for MPTCP subpaths; and (4) we study and improve the algorithm of multihop routing in MANETs. The test results show that our algorithms can offer more efficient use of multiple subpaths and better network traffic load balancing than using standard MPTCP alone. INDEX TERMS Data delivery, hidden Markov, MANET, multipath routing, multipath TCP, quality of experience.