Electrochemical Synthesis Of Polymer Monolayer And Its Conductive Properties

The functions and properties of polymers are not only dependent on their chemical structure,but also closely on the orientation and arrangement.The regulation of ordered structure is an effective way to achieve high-performance polymer materials.The preparation of ideal monolayers with thickness equivalent to the theoretical length of the polymer has been a formidable challenge because of the spatial kinetic and statistical restrictions in the synthesis and manipulation process.The methods that could achieve polymer monolayers include polymer surface grafting,surface initiated polymerization,and solid phase iterative synthesis.The first method can use the pre-synthesized polymer to graft onto the substrate surface,but generally results in insufficient coverage and low molecular density.The second method has a low initiation percentage of surface reactions because of spatial dynamics and statistical competition in chains growth.The third method shows formidable challenge in the synthesis of complex structural and functional polymers because of its low heterogeneous reactions efficiency of solid/liquid interface and incapable reparability in iterative defects.The electrochemical iterative synthesis method developed by us can improve simultaneously the interface reaction rate and repair iterative defects,providing a prerequisite for the preparation of ideal polymer monolayers.The results demonstrate that the unidirectional oriented polymer crystalline monolayers have approached the maximum physical limit and with rich electrical parameters regulation capabilities.The main contents and results are as follows:(1)Electrochemical iterative synthesis is a kinetic and statistical allowing method of surface initiated parallel synthesis and uniform synthesis.we repair the iterative defects by repeating the same electrochemical iterative reaction,statistically ensuring the highly parallel and uniform synthesis of polymer monolayers.The thickness of the polymer monolayer after 9 iterations of terpyridine ruthenium monomer is 22 nm,and equivalent to the theoretical molecular length(22 nm).The roughnesses of the crystalline monolayers are less than 0.64 nm,and the maximum height change on the surface is comparable with the length of monomer.The modulus and current density of polymer crystalline monolayer can reach 40 and 1000 times higher than their amorphous counterpart.We reason that the density,modulus,and conductance of the monolayer reach the physical limits of the polymer structure.The nonlinear conductance of monolayers exhibits the bias-and length-dependent current hysteresis and negative differential resistance(NDR)effect.Electrochemical iterative synthesis can also synthesize single polymer chain with a scalable molecular length by regulating the proportion of electroactive monomers in self-assembled monolayers,and demonstrated by single-molecule force spectroscopy.(2)Electrochemical iterative synthesis can simultaneously achieve polymer synthesis and ordered arrangement,providing a new strategy for the preparation of macroscopically crystalline polymers.The thickness of the polymer monolayer after 17 iterations is 30 nm,and similar to the theoretical molecular length.The roughnesses of monolayers are less than 0.65 nm,and the maximum height change on the surface is similar to the length of monomer.These monolayers exhibit length-dependent conductive and electrocatalytic behaviors.With the increasing of the molecular length,the current density of the monolayers decreases by 2 orders of magnitude,while the electrocatalytic performance increases and then decreases.The length-dependent conductive and electrocatalytic relationships provide a molecular design approach for the optimization of the catalytic performance of prototypical molecules.The conductance decay constants β value of monolayers is 0.063 nm-1,which is the minimum value of reported monolayers literature.(3)The synthesis of unidirectionally oriented uniform polymer monolayers provides a prerequisite for the study of sequence-controlled polymer monolayers,and these monolayers can greatly restrict the stochasticity and instability of conductive filaments.The conductance of monolayers mainly depends on the metal species,while the sequence becomes a matter in multicomponent polymer monolayers.Specifically,the conductance orders of monolayers are AB diblock structure>AABB alternating structure>AB alternating structure,and ABC triblock structure>ABC alternating structure.Polymer monolayers with controllable length,monomer composition,and sequence show an ultra-rich variety of nonlinear conductive behaviors and functions regulation capabilities.Specifically,these monolayers show both ranges of current density and on/off ratio in the four orders of magnitude.The maximum values of nonlinear response NDR effect parameters RPtV and Ron/off are 15.8 and 1000,respectively,and they are one of the highest reported values.