You can become a member by joining one of the two groups:
SCI Colloid & Surface Chemistry Group (CSCG). http://www.soci.org/Membership-and-Networks/Technical-Groups/Colloid-and-Surface-Chemistry-Group
RSC Colloid & Interface Science Group (CISG). http://www.rsc.org/membership/networking/InterestGroups/colloidscience/
The former is open to SCI members only. The latter is open both to RSC members and associates AND to scientists and engineers who belong, either, to a chartered professional or learned body from outside the chemical sciences, or to another chemical society with whom the RSC has entered into an international partnership agreement approved by RSC Council. Non-RSC members of CISG pay RSC a small annual fee to cover administration and postage.
For information on how to become a member of the Society of Chemical Industry (SCI) or Royal Society of Chemistry (RSC) please see the links below:
Non-members of RSC wishing to join CISG should contact the RSC Membership Dept. (contact details at http://www.rsc.org/Membership/join/admission/Contacts.asp), asking to join the Colloid & Interface Science Interest Group, only, and mentioning their own affiliation. The membership administration fee is £10 currently. In case of difficulty please contact a member of the Joint Committee.