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Rechargeable aqueous zinc-ion batteries (RAZIBs) have some inherent advantages such as intrinsic safety, low-cost and theoretically high energy density, making them a current topic of interest. However, the phenomenon of zinc (Zn) dendrite growth at the anode results in the instability of RAZIBs and limits their real-world application. Herein, by employing a high strength hydrogel polymer electrolyte, the growth of dendritic Zn crystals is effectively eliminated through the mechanical suppression effect, resulting in a stable Zn anode that demonstrates dendrite-free plating/stripping with a long lifespan. Even under a high current density of 5 mA cm(-2), the Zn||Zn symmetric cell is shown to have a cyclic lifetime of longer than 1000 hours. Moreover, the stable cyclic performance of the Zn anode spawns a Zn||MnO2 battery with high capacity (4.8-1.9 mA h cm(-2)) and long lifetime (500 cycles at 9.2 mA cm(-2), 1C), which can meet the practical demands for portable devices. This work shows that high strength polymer gel electrolytes with internal energy dissipation mechanisms can overcome previous challenges that prevented practical utilization of RAZIBs. Together with the outstanding cyclic properties of the high capacity Zn||MnO2 batteries, this work provides a new pathway toward designing high energy density RAZIBs.

The high water content of hydrogels makes them important as synthetic biomaterials, and tuning the mechanical properties of hydrogels to match those of natural tissues without changing chemistry is usually difficult. In this study, we have developed a series of hydrogels with varied stiffness, strength, and toughness based on a combination of poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS), a strong acidic polyelectrolyte, and poly-N-(carboxymethyl)-N,N-dimethyl-2-(methacryloyloxy) ethanaminium) (PCDME), a polyzwitterion with a weak acidic moiety. We demonstrate that modifying the true molar ratio, R, of PCDME to PAMPS results in four unique categories of hydrogels with different swelling ratios and Young’s moduli. When R < 1, a negatively charged polyelectrolyte gel (PE) is formed; when 1 < R < 3, a tough and viscoelastic polyelectrolyte complex gel (PEC) is formed; when 3 < R < 6.5, a conventional, elastic interpenetrating network gel (IPN) is formed; and when R > 6.5, a tough and stiff double-network gel (DN) is formed. Both the PEC and DN gels exhibit high toughness and fracture stress, up to 1.8 and 1.5 MPa, respectively. Importantly, the PEC gels exhibit strong recovery properties along with high toughness, distinguishing them from DN gels. Without requiring a change in chemistry, we can tune the mechanical response of hydrogels over a wide spectrum, making this a useful system of soft and hydrated iomaterials.

In this work, we develop a series of novel elastomers from acrylate monomers by one-step free radical copolymerization without using organic solvents. The dynamics of the elastomers, characterized by the Kuhn segment relaxation time τ0, is tuned over six orders of magnitude by varying the structure and composition of the acrylate monomers. Comprehensive studies on linear rheology at small deformation and tensile/fracture behaviors at large deformation of the materials are performed. A universal ductile–brittle transition of the elastomers with the criterion of [small epsi, Greek, dot above]τ0 ≂ 0.1 is observed for the diverse monomer pairs and stretch–strain rate [small epsi, Greek, dot above] and the elastomers exhibit maximum energy dissipation around the ductile–brittle transition reaching a work of extension at fracture of ∼25 MJ m−3 and a fracture energy of 20 kJ m−2. Such toughness is comparable to that of natural rubbers and is among the highest ever reported. In addition, these elastomers possess 100% self-recovery, and a relatively high self-healing efficiency (37–70%) of the cut samples at room temperature even for relatively rigid samples and strong adhesive strength on glass and polymethylmethacrylate (PMMA) substrates. The universal ductile–brittle transition of the materials means that we can use the linear rheology dynamics as fingerprints for predicting the dynamic spectra of toughness of the materials. The wide range of tunable dynamics substantially enriches the choice of elastomers for various applications, and the facile and solvent-free synthesis of these elastomers is eco-friendly, cost-effective and scalable, which greatly lowers the barrier for practical applications.

This dissertation focuses on two important areas in wireless communications: receiver design and security. In the first part of this dissertation we consider low data rate receiver design for ultra-wideband (UWB), a wideband radio technology that promises to help solve the frequency allocation problem that often inhibits narrowband systems. Reference-based receivers are promising candidates in the UWB regime, because the conventional rake receiver designs suffers from complexity limitations and inaccuracies in channel estimation. Many reference-based systems have arisen as viable solutions for receivers. We unify these systems as well as other systems into the general framework for performance analysis to suggest the optimal system for varying constraints. We improve the performance of frequency-shifted reference (FSR-UWB) for an average power constraint by halving the frequency offset and employing a sample-and-hold approach across the frame period. Also, we introduce a novel peak mitigation technique; tone reservation, for the multi-differential (MD) version of FSR-UWB, to reduce the high peak-to-average power ratio observed as the data carriers increase. The next part of this dissertation is about wireless security which is ubiquitous in modern news. Cryptography is widely use for security but it assumes limited computational abilities of an eavesdropper, is based on the unproven hardness of the underlying primitives, and allows for the message to be recorded and decrypted later. In this dissertation we consider an information-theoretic security approach to guaranteeing everlasting secrecy. We contribute a new secrecy rate pair outage formulation, where an outage event is based on the instantaneous rates of the destination and the eavesdropper being below and above desired thresholds, respectively. In our new secrecy rate pair outage formulation, two new unaccounted outage events emerge: secrecy breach, where the eavesdropper is above the targeted threshold; unreliable, where the destination is unable to successfully decode the message. The former case must be carefully avoided, while for the latter case we can exploit automatic retransmissions (ARQ) while maintaining the eavesdropper intercept probability below the target threshold. We look at both ``simple'' receivers and also complex receivers that use a buffer to store previous messages to maximally combine signal-to-noise ratio (SNR). Then we extend these results to the two-hop case where we maximize the end-to-end secure throughput by optimizing the intercept probability at each eavesdropper given a total end-to-end intercept constraint. Lastly, we consider the difficult case in information-theoretic security: the near eavesdropper case, where we contribute an optimal power allocation algorithm that leverages nearby chatter nodes to generate noise to reduce the probability of intercept by the eavesdropper while minimally impeding the source-to-destination communication. As shown in both one-hop and two-hop cases, allowing a slight outage at the destination for cases of when the eavesdropper is above a specific threshold greatly improves secrecy performance.