A Surface Forces Apparatus (SFA) 2000 (SurForce LLC, Goleta, CA, USA) was used with a normal force measuring configuration. Spring constants were changed for each reported condition using either a weak, intermediate, or stiff spring with spring constants of kweak ≈ 1,000 N/m, kintermediate ≈ 2,500 N/m, or kstiff ≈ 13,000 N/m, respectively. Humidity was monitored with a Rotronic HC2A-IC industrial humidity probe mounted to the SFA chamber. Details on the multiple beam interference (MBI) technique and force-distance measurement technique of the SFA can be found elsewhere.