Partial monolayers of uniform length alkyl chains [CH3(CH2)(n)-;n=10-21] bonded at constant coverage onto a disordered lattice of silanol groups on amorphous SiO2, exhibit a distinct change in surface wetting behavior for 14 less than or equal to n less than or equal to 17 which correlates closely with a significant shift in the average conformational ordering of the chains. These data provide definitive evidence for the existence of a family of surface-constrained, intermediately ordered phases of discrete length, flexible chains and imply that broad classes of these families exist.