Effect Of Hydrophobic Micro - Block Length On The Interaction Of Micro - Block Hydrophobic Association Polyacrylamide With Sodium Dodecyl Sulfate

The binary system composed of hydrophobically associating polymers and surfactants has enormous application potential in EOR. However, the control for the performance of these polymer/surfactant systems at an appropriate range is a key point in field applications, so as to guarantee a good injectivity, solution stability and rheological properties of these systems. Therefore, a combination of experiments involving associative effect, binding capacity and oil-water interface performance was applied to investigate the effect of hydrophobic micro-block length on the interaction between the hydrophobically associating polyacrylamide and the sodium dodecyl sulfate (SDS), which will be expected to find an appropriate amount of surfactant and the match of the optimal micro-block length for polymers and provide the theoretical guidance for practical applications. The main contents are as follows:First, on the basic of an adjusting mechanism for the hydrophobic microblock length with a lower alcohol was established, the microblock hydrophobically associating polyacrylamides (MBHAPs) with different micro-block length were prepared by the radical copolymerization of a low amount (0.5 mol%) of cetyl dimethyl ammonium chloride (C16DMAAC) and acrylamide (AM) initiated by compound initiator at 30℃ and final hydrolyzation with sodium hydroxide, the molecular structure was characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectrogram (’HNMR) to demonstrate the presence of hydrophobic monomers in the polymer; the ion titration experiment was carried out to determine the actual hydrophobe content in the polymer and the data show that the content is almost the same; the effects of polyelectrolyte and association were eliminated and shielded with NaCl and formamide to obtain the reference viscosity average molecular weight of the polymers, the molecular weight are almost the same. All results confirmed that the MBHAPs have the consistency excepted the micro-block, i.e., the differences of the microblock are indeed exist in MBHAPs.Secondly, the self-association effect of MBHAPs was investigated by the rheological measurements. The results show that with the increase of microblock length, the self-association effect of MBHAPs gradually increased, indicating the block is longer, the degree of intermolecular association is more obvious, the ablility to form a larger physical crosslinking network is stronger, the contribution made by the solution structure to the viscosity is greater. Moreover, the association effects of MBHAPs/SDS systems were studied combining rheological test and steady-state fluorescence spectroscopy. The magnitudes of viscosity reduction or enhancement of system in different solution regions show that when the block length is longer, the system is provided with the stronger association effect, the magnitude of viscosity reduction is smaller at low polymer concentration, the thickening magnitude is larger at higher concentrations. With microblock length increases, the I3/I1, Ie/Im and extreme peaks of the system all present the increasing trends, which indicate that, the effect of SDS to accelerate polymer association is more obvious, the tightness of hydrophobic microdomains is greater, a large number of hydrophobic microdomains hydrophobic microdomains can be formed earlier and ultimately the number of microdomains is largest. What the most interesting, however, is that the viscosity in the whole de-viscosity or thickening process and the Ie/Im of different MBHAPs/SDS system all appear two significant increasing trend, that is, "Twin Peaks" phenomenon, which no one has yet reported and its generation mechanism is not clear. It may be caused by some charge interaction between the cationic polymer and the anionic surfactant, but it needs to be demonstrated from other experiments.Meanwhile, the cmc of the SDS in pure SDS solution and MBHAPs/SDS system was respectively determined using surface tension measurements and conductivity experiments, through comparative analysis of the difference between the two cmc to calculate the binding capacity of SDS in system. As a consequence, a feasible method to determine the binding capacity of SDS in polymer/SDS system was established. The results show that with the increase of the hydrophobic block lengths the binding capcity between polymers and SDS decreases, when the system reaches saturation binding, a hydrophobic side chain of the polymer with shortest microblock can bind average 5-10 SDS molecules, in contrast,1-4 SDS molecules can be combined.Finally, the oil-water interface properties of MBHAPs solutions and MBHAPs/ SDS systems were investigated by the Zeta potential at n-octane-water interface. The results show that with increasing MBHAPs concentration zeta potential occurs a charge reversal phenomenon, the block length increases slightly, the negative zeta potential reduces and the charge reversal advances. At three particular and different polymer concentrations, the effect of MBHAPs/SDS system on the zeta potential also presents the charge reversal phenomenon to a certain extend, i.e., the absolute value of zeta potential reduces rapidly and tends to zero at a lower SDS concentration rang with the addition of SDS, and then present negative charge and gradually increases at a larger SDS concentration region. In addition, with the increase of microblock length, the zeta potential at droplet surface changs from the initial positive charge to the negative charge rapidly; with increasing polymer concentration, at the same SDS concentration, the absolute value of zeta potential also increases. Possible mechanisms for these phenomena and results are introduced and discussed.