DNA nanotubes(DNTs)with user-defined shapes and functionalities have potential applications in many fields.So far,compared with numerous experimental studies,there have been only a handful of models on the mechanical properties of such DNTs.This paper aims at presenting a multiscale model to quantify the correlations among the pre-tension states,tensile properties,encapsulation structures of DNTs,and the surrounding factors.First,by combining a statistical worm-like-chain(WLC)model of single DNA deformation and Parsegian's mesoscopic model of DNA liquid crystal free energy,a multiscale tensegrity model is established,and the pre-tension state of DNTs is characterized theoretically for the first time.Then,by using the minimum potential energy principle,the force-extension curve and tensile rigidity of pre-tension DNTs are predicted.Finally,the effects of the encapsulation structure and surrounding factors on the tensile properties of DNTs are studied.The predictions for the tensile behaviors of DNTs can not only reproduce the existing experimental results,but also reveal that the competition of DNA intrachain and interchain interactions in the encapsulation structures determines the pre-tension states of DNTs and their tensile properties.The changes in the pre-tension states and environmental factors make the monotonic or non-monotonic changes in the tensile properties of DNTs under longitudinal loads.
Time-dependent behaviors due to various mismatch strains are very important to the reliability of micro-/nano-devices.This paper aims at presenting an analytical model to study the viscoelastic stress relaxation of the laminated microbeam caused by mismatch strain.Firstly,Zhang’s two-variable method is used to establish a mechanical model for predicting the quasi-static stress relaxation of the laminated microbeam.Secondly,the related analytical solutions are obtained by combining the differential method and the eigenvalue method in the temporal domain.Finally,the influence of the substrateto-film thickness/modulus ratio on the relaxation responses of the laminated microbeam subject to a step load of the mismatch strain is studied.The results show that the present predictions are consistent with the previous theoretical studies.Furthermore,the thickness dependence of stress relaxation time of the laminated microbeam is jointly determined by the intrinsic structural evolution factors and tension-bending coupling state;the stress relaxation time can be controlled by adjusting the substrate-to-film thickness/modulus ratio.
Boundary constraint induced inhomogeneous effects are important for mechanical responses of nano/micro-devices.For microcantilever sensors,the clamped-end constraint induced inhomogeneous effect of static deformation,so called the clamped-end effect,has great influence on the detection signals.This paper is devoted to developing an alternative mechanical model to characterize the clamped-end effect on the static detection signals of the DNA-microcantilever.Different from the previous concentrated load models,the DNA adsorption is taken as an equivalent uniformly distributed tangential load on the substrate upper surface,which exactly satisfies the zero force boundary condition at the free-end.Thereout,a variable coefficient differential governing equation describing the non-uniform deformation of the DNA-microcantilever induced by the clamped-end constraint is established by using the principle of minimum potential energy.By reducing the order of the governing equation,the analytical solutions of the curvature distribution and static bending deflection are obtained.By comparing with the previous approximate surface stress models,the clamped-end effect on the static deflection signals is discussed,and the importance of the neutral axis shift effect is also illustrated for the asymmetric laminated microcantilever.
